Build with sassc

This removes the sass depedency of this gem and instead replaces it with
a sassc-rails dependency. This is set as a development dependency as
this is only required for the dummy version of this app and this gem
should not force a particular version of sass on consuming apps without
good reason.

This should help GOV.UK gradually move towards a world without Ruby
SASS. Prior to this change introducing govuk_publishing_components into
an application forced Ruby SASS in as a dependency, this has the effect
in Sprockets of choosing Ruby SASS over sassc.

A downside of doing this is that it will make the warm cache run slower
for requests. Until GOV.UK Frontend resolves some performance issues [1]
we may find each page of the dummy app loads a reasonable amount slower
in a development environment. Although not ideal, I don't think this
performance issue will cause anyone significant problems developing on
this app (I get about 2.5s on my local machine) and it'll be nice for us
to have already started the sassc journey.

[1]: alphagov/govuk-frontend#1671

Gemfile.lock

@@ -9,8 +9,6 @@ PATH
       rails (>= 5.0.0.1)
       rake
       rouge
-      sass (= 3.7.4)
-      sassc-rails (>= 2.0.1)
       sprockets (< 4)
 
 GEM
@@ -61,9 +59,9 @@ GEM
       public_suffix (>= 2.0.2, < 5.0)
     arel (9.0.0)
     ast (2.4.0)
-    brakeman (4.8.0)
+    brakeman (4.8.1)
     builder (3.2.4)
-    byebug (11.1.1)
+    byebug (11.1.3)
     capybara (3.32.1)
       addressable
       mini_mime (>= 0.1.3)
@@ -134,7 +132,7 @@ GEM
       activesupport (>= 4.0)
       logstash-event (~> 1.2.0)
       request_store
-    loofah (2.4.0)
+    loofah (2.5.0)
       crass (~> 1.0.2)
       nokogiri (>= 1.5.9)
     mail (2.7.1)
@@ -144,7 +142,7 @@ GEM
     method_source (1.0.0)
     mime-types (3.3.1)
       mime-types-data (~> 3.2015)
-    mime-types-data (3.2019.1009)
+    mime-types-data (3.2020.0425)
     mimemagic (0.3.4)
     mini_mime (1.0.2)
     mini_portile2 (2.4.0)
@@ -160,7 +158,7 @@ GEM
       ast (~> 2.4.0)
     phantomjs (2.1.1.0)
     plek (3.0.0)
-    pry (0.13.0)
+    pry (0.13.1)
       coderay (~> 1.1)
       method_source (~> 1.0)
     pry-byebug (3.9.0)
@@ -201,9 +199,6 @@ GEM
     rainbow (3.0.0)
     raindrops (0.19.1)
     rake (13.0.1)
-    rb-fsevent (0.10.3)
-    rb-inotify (0.10.1)
-      ffi (~> 1.0)
     regexp_parser (1.7.0)
     request_store (1.5.0)
       rack (>= 1.4)
@@ -255,12 +250,7 @@ GEM
     ruby-progressbar (1.10.1)
     rubyzip (2.3.0)
     safe_yaml (1.0.5)
-    sass (3.7.4)
-      sass-listen (~> 4.0.0)
-    sass-listen (4.0.0)
-      rb-fsevent (~> 0.9, >= 0.9.4)
-      rb-inotify (~> 0.9, >= 0.9.7)
-    sassc (2.2.1)
+    sassc (2.3.0)
       ffi (~> 1.9)
     sassc-rails (2.1.2)
       railties (>= 4.0.0)
@@ -292,10 +282,10 @@ GEM
       unf_ext
     unf_ext (0.0.7.7)
     unicode-display_width (1.7.0)
-    unicorn (5.5.4)
+    unicorn (5.5.5)
       kgio (~> 2.6)
       raindrops (~> 0.7)
-    webdrivers (4.2.0)
+    webdrivers (4.3.0)
       nokogiri (~> 1.6)
       rubyzip (>= 1.3.0)
       selenium-webdriver (>= 3.0, < 4.0)
@@ -324,6 +314,7 @@ DEPENDENCIES
   pry-byebug
   rspec-rails (~> 4.0)
   rubocop-govuk (~> 3)
+  sassc-rails (~> 2)
   selenium-webdriver (= 3.142.7)
   uglifier (>= 4.1.0)
   webmock (~> 3.8.3)

govuk_publishing_components.gemspec

@@ -22,8 +22,6 @@ Gem::Specification.new do |s|
   s.add_dependency "rails", ">= 5.0.0.1"
   s.add_dependency "rake"
   s.add_dependency "rouge"
-  s.add_dependency "sass", "3.7.4"
-  s.add_dependency "sassc-rails", ">= 2.0.1"
   s.add_dependency "sprockets", "< 4"
 
   s.add_development_dependency "capybara", "~> 3.25"
@@ -35,6 +33,7 @@ Gem::Specification.new do |s|
   s.add_development_dependency "pry-byebug"
   s.add_development_dependency "rspec-rails", "~> 4.0"
   s.add_development_dependency "rubocop-govuk", "~> 3"
+  s.add_development_dependency "sassc-rails", "~> 2"
   s.add_development_dependency "selenium-webdriver", "= 3.142.7"
   s.add_development_dependency "uglifier", ">= 4.1.0"
   # Webmock is needed to load slimmer test helpers