Update Faraday to v1.0

[epistrephein]

Pull Request description

• Update the minimum version of faraday dependency to v1.0
• Remove faraday_middleware dependency and use native JSON lib to parse responses
• Bump minimum Ruby version to 2.3
• Remove sudo: false from .travis.yml (Explanation)
• Update RuboCop version of Hound to 0.75 and remove Gemspec/RequiredRubyVersion rule
• Minor style fixes

Pull Request checklist

Kind of change

• My code is a minor change (typos, configuration, anything not related to core functionality)
• My code is a bug fix (non-breaking change which fixes an issue)
• My code is a new feature (non-breaking change which adds functionality)
• My code introduces a breaking change (fix or feature that would break existing functionality)

Style and tests

• My code follows the code style of this project
• I have added tests to cover my changes
• All new and existing tests passed

Documentation

• My change requires a change to the documentation
• I have updated the documentation accordingly

Changelog

• I have included the CHANGELOG entry for the changes

[epistrephein]

On hold until official GitHub release of Faraday v1.0.
Released: v1.0.0