Update project to use defra_ruby_style (#28)

Updated the project to use our new shared gem for managing our ruby style rules.

.rubocop.yml

@@ -1,97 +1,3 @@
-AllCops:
-  TargetRubyVersion: 2.4
-  # Cop names are not displayed in offense messages by default. We find it
-  # useful to include this information so we can use it to investigate what the
-  # fix may be.
-  DisplayCopNames: true
-  # Style guide URLs are not displayed in offense messages by default. Again we
-  # find it useful to go straight to the documentation for a rule when
-  # investigating what the fix may be.
-  DisplayStyleGuide: true
-  Include:
-    - "**/*.gemspec"
-    - "**/*.rake"
-    - "**/*.rb"
-    - "**/Gemfile"
-    - "**/Rakefile"
-    - "**/config.ru"
-  Exclude:
-    # config contains standard files created when Rails is initialised and
-    # therefore they should be left as is
-    - "**/config/**/*"
-    # bin contains standard files created when Rails is initialised and
-    # therefore they should be left as is
-    - "**/bin/*"
-    # locally when we run rubocop it ignores the vendor folder but when running
-    # in Travis-CI it seems to include. This will stop this from happening
-    - "**/vendor/**/*"
-    ## schema.rb is generated automatically based on migrations, so leave as is
-    - "**/db/schema.rb"
-    # Skip dummy application files as they're only used for testing purposes
-    - "spec/dummy/**/*"
-
-# It is our opinion that code is easier to read if a white space is
-# permitted between the initial declaration and the first statement. Ditto the
-# last statement and the closing tag.
-Layout/EmptyLinesAroundModuleBody:
-  Enabled: false
-Layout/EmptyLinesAroundClassBody:
-  Enabled: false
-Layout/EmptyLinesAroundBlockBody:
-  Enabled: false
-
-# We felt as a team that the default size of 15 was too low, and blocked what to
-# us are sound methods which would not add any value if broken up, for example
-# composer type methods. Therefore we agreed to up the score to 30 to allow for
-# these types of methods
-Metrics/AbcSize:
-  Max: 30
-
-# We don't feel it makes sense to split specs and factories over multiple files,
-# or when in a context be forced to try and come up with slightly different ones
-# in order to reduce the block length. Hence we exclude specs and factories from
-# this rule.
-# Shared examples are the same as specs, but don't have the _spec.rb extension
-# hence they are listed separately
-Metrics/BlockLength:
-  Exclude:
-    # We're not bothered about a gemspec file having long block length
-    - "*.gemspec"
-    - "**/spec/**/*_spec.rb"
-    - "**/spec/factories/**/*.rb"
-    - "**/spec/support/shared_examples/*.rb"
-
-# We believe the default 80 characters is too restrictive and that lines can
-# still be readable and maintainable when no more than 120 characters. This also
-# allows us to maximise our screen space.
-Metrics/LineLength:
-  Max: 120
-  Exclude:
-    - "**/spec/**/*_spec.rb"
-    - "**/spec/factories/**/*.rb"
-    - "**/spec/support/shared_examples/*.rb"
-
-# We wish we were good enough to remain within the rubocop limit of 10 lines
-# however we often just seem to tip over by a few lines. Hence we have chosen
-# to bump it to 20.
-Metrics/MethodLength:
-  Max: 20
-
-# Spec files can be quite long, so we shouldn't be forced to break them up
-# if it doesn't make sense.
-Metrics/ModuleLength:
-  Exclude:
-    - "**/spec/**/*_spec.rb"
-    - "**/spec/factories/**/*.rb"
-    - "**/spec/support/shared_examples/*.rb"
-
-# As long as the team commit to using well named classes for it should not be
-# necessary to add top-level class documentation.
-Style/Documentation:
-  Enabled: false
-
-# There are no relative performance improvements using '' over "", therefore we
-# believe there is more value in using "" for all strings irrespective of
-# whether string interpolation is used
-Style/StringLiterals:
-  EnforcedStyle: double_quotes
+inherit_gem:
+  defra_ruby_style:
+    - default.yml

os_map_ref.gemspec

@@ -25,6 +25,7 @@ Gem::Specification.new do |s|
 
   s.required_ruby_version = ">= 2.4"
 
+  s.add_development_dependency "defra_ruby_style"
   # Allows us to automatically generate the change log from the tags, issues,
   # labels and pull requests on GitHub. Added as a dependency so all dev's have
   # access to it to generate a log, and so they are using the same version.
@@ -34,6 +35,5 @@ Gem::Specification.new do |s|
   s.add_development_dependency "github_changelog_generator"
   s.add_development_dependency "rake"
   s.add_development_dependency "rspec", "~> 3.8"
-  s.add_development_dependency "rubocop"
   s.add_development_dependency "simplecov"
 end