Update to handle latest Flutter

.github/ISSUE_TEMPLATE/bug_report.md

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+---
+name: Bug report
+about: There is a problem in how provider behaves
+title: ""
+labels: bug, needs triage
+---
+
+**Describe the bug**
+A clear and concise description of what the bug is.
+
+**To Reproduce**
+
+<Please add a small sample to that can be executed to reproduce the problem. As a general rule, 100 lines is the maximum>
+
+**Expected behavior**
+A clear and concise description of what you expected to happen.

.github/ISSUE_TEMPLATE/config.yml

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+blank_issues_enabled: false
+contact_links:
+  - name: I have a problem and I need help
+    url: https://stackoverflow.com/questions/tagged/flutter

.github/ISSUE_TEMPLATE/example_request.md

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+---
+name: Documentation improvement request
+about: >-
+  Suggest a new example/documentation or ask for clarification about an
+  existing one.
+title: ""
+labels: documentation, needs triage
+---
+
+**Describe what scenario you think is uncovered by the existing examples/articles**
+A clear and concise description of the problem that you want explained.
+
+**Describe why existing examples/articles do not cover this case**
+Explain which examples/articles you have seen before making this request, and
+why they did not help you with your problem.
+
+**Additional context**
+Add any other context or screenshots about the documentation request here.

.github/ISSUE_TEMPLATE/feature_request.md

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+---
+name: Feature request
+about: Suggest an idea for this project
+title: ""
+labels: enhancement, needs triage
+---
+
+**Is your feature request related to a problem? Please describe.**
+A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
+
+**Describe the solution you'd like**
+A clear and concise description of what you want to happen.
+
+**Describe alternatives you've considered**
+A clear and concise description of any alternative solutions or features you've considered.
+
+**Additional context**
+Add any other context or screenshots about the feature request here.

.github/workflows/build.yml

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+name: Build
+
+on: [push, pull_request]
+
+jobs:
+  flutter:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        package:
+          - .
+          - /example
+        channel:
+          - dev
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - uses: subosito/flutter-action@v1
+        with:
+          channel: ${{ matrix.channel }}
+
+      - name: Install dependencies
+        run: flutter pub get
+        working-directory: ${{ matrix.package }}
+
+      - name: Check format
+        run: flutter format --set-exit-if-changed .
+        working-directory: ${{ matrix.package }}
+
+      - name: Analyze
+        run: flutter analyze
+        working-directory: ${{ matrix.package }}
+
+      - name: Run tests
+        run: flutter test
+        working-directory: ${{ matrix.package }}

all_lint_rules.yaml

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+linter:
+  rules:
+    - always_declare_return_types
+    - always_put_control_body_on_new_line
+    - always_put_required_named_parameters_first
+    - always_require_non_null_named_parameters
+    - always_specify_types
+    - always_use_package_imports
+    - annotate_overrides
+    - avoid_annotating_with_dynamic
+    - avoid_as
+    - avoid_bool_literals_in_conditional_expressions
+    - avoid_catches_without_on_clauses
+    - avoid_catching_errors
+    - avoid_classes_with_only_static_members
+    - avoid_double_and_int_checks
+    - avoid_empty_else
+    - avoid_equals_and_hash_code_on_mutable_classes
+    - avoid_escaping_inner_quotes
+    - avoid_field_initializers_in_const_classes
+    - avoid_function_literals_in_foreach_calls
+    - avoid_implementing_value_types
+    - avoid_init_to_null
+    - avoid_js_rounded_ints
+    - avoid_null_checks_in_equality_operators
+    - avoid_positional_boolean_parameters
+    - avoid_print
+    - avoid_private_typedef_functions
+    - avoid_redundant_argument_values
+    - avoid_relative_lib_imports
+    - avoid_renaming_method_parameters
+    - avoid_return_types_on_setters
+    - avoid_returning_null
+    - avoid_returning_null_for_future
+    - avoid_returning_null_for_void
+    - avoid_returning_this
+    - avoid_setters_without_getters
+    - avoid_shadowing_type_parameters
+    - avoid_single_cascade_in_expression_statements
+    - avoid_slow_async_io
+    - avoid_types_as_parameter_names
+    - avoid_types_on_closure_parameters
+    - avoid_unnecessary_containers
+    - avoid_unused_constructor_parameters
+    - avoid_void_async
+    - avoid_web_libraries_in_flutter
+    - await_only_futures
+    - camel_case_extensions
+    - camel_case_types
+    - cancel_subscriptions
+    - cascade_invocations
+    - close_sinks
+    - comment_references
+    - constant_identifier_names
+    - control_flow_in_finally
+    - curly_braces_in_flow_control_structures
+    - diagnostic_describe_all_properties
+    - directives_ordering
+    - do_not_use_environment
+    - empty_catches
+    - empty_constructor_bodies
+    - empty_statements
+    - exhaustive_cases
+    - file_names
+    - flutter_style_todos
+    - hash_and_equals
+    - implementation_imports
+    - invariant_booleans
+    - iterable_contains_unrelated_type
+    - join_return_with_assignment
+    - leading_newlines_in_multiline_strings
+    - library_names
+    - library_prefixes
+    - lines_longer_than_80_chars
+    - list_remove_unrelated_type
+    - literal_only_boolean_expressions
+    - missing_whitespace_between_adjacent_strings
+    - no_adjacent_strings_in_list
+    - no_default_cases
+    - no_duplicate_case_values
+    - no_logic_in_create_state
+    - no_runtimeType_toString
+    - non_constant_identifier_names
+    - null_closures
+    - omit_local_variable_types
+    - one_member_abstracts
+    - only_throw_errors
+    - overridden_fields
+    - package_api_docs
+    - package_names
+    - package_prefixed_library_names
+    - parameter_assignments
+    - prefer_adjacent_string_concatenation
+    - prefer_asserts_in_initializer_lists
+    - prefer_asserts_with_message
+    - prefer_collection_literals
+    - prefer_conditional_assignment
+    - prefer_const_constructors
+    - prefer_const_constructors_in_immutables
+    - prefer_const_declarations
+    - prefer_const_literals_to_create_immutables
+    - prefer_constructors_over_static_methods
+    - prefer_contains
+    - prefer_double_quotes
+    - prefer_equal_for_default_values
+    - prefer_expression_function_bodies
+    - prefer_final_fields
+    - prefer_final_in_for_each
+    - prefer_final_locals
+    - prefer_for_elements_to_map_fromIterable
+    - prefer_foreach
+    - prefer_function_declarations_over_variables
+    - prefer_generic_function_type_aliases
+    - prefer_if_elements_to_conditional_expressions
+    - prefer_if_null_operators
+    - prefer_initializing_formals
+    - prefer_inlined_adds
+    - prefer_int_literals
+    - prefer_interpolation_to_compose_strings
+    - prefer_is_empty
+    - prefer_is_not_empty
+    - prefer_is_not_operator
+    - prefer_iterable_whereType
+    - prefer_mixin
+    - prefer_null_aware_operators
+    - prefer_relative_imports
+    - prefer_single_quotes
+    - prefer_spread_collections
+    - prefer_typing_uninitialized_variables
+    - prefer_void_to_null
+    - provide_deprecation_message
+    - public_member_api_docs
+    - recursive_getters
+    - sized_box_for_whitespace
+    - slash_for_doc_comments
+    - sort_child_properties_last
+    - sort_constructors_first
+    - sort_pub_dependencies
+    - sort_unnamed_constructors_first
+    - test_types_in_equals
+    - throw_in_finally
+    - type_annotate_public_apis
+    - type_init_formals
+    - unawaited_futures
+    - unnecessary_await_in_return
+    - unnecessary_brace_in_string_interps
+    - unnecessary_const
+    - unnecessary_final
+    - unnecessary_getters_setters
+    - unnecessary_lambdas
+    - unnecessary_new
+    - unnecessary_null_aware_assignments
+    - unnecessary_null_in_if_null_operators
+    - unnecessary_nullable_for_final_variable_declarations
+    - unnecessary_overrides
+    - unnecessary_parenthesis
+    - unnecessary_raw_strings
+    - unnecessary_statements
+    - unnecessary_string_escapes
+    - unnecessary_string_interpolations
+    - unnecessary_this
+    - unrelated_type_equality_checks
+    - unsafe_html
+    - use_full_hex_values_for_flutter_colors
+    - use_function_type_syntax_for_parameters
+    - use_is_even_rather_than_modulo
+    - use_key_in_widget_constructors
+    - use_late_for_private_fields_and_variables
+    - use_raw_strings
+    - use_rethrow_when_possible
+    - use_setters_to_change_properties
+    - use_string_buffers
+    - use_to_and_as_if_applicable
+    - valid_regexps
+    - void_checks