Merge pull request #321 from alphagov/dependabot/bundler/rubocop-govuk-eq-4.18.0

Update rubocop-govuk requirement from = 4.17.1 to = 4.18.0

Author: brucebolt

govspeak.gemspec

@@ -42,6 +42,6 @@ library for use in the UK Government Single Domain project'
   s.add_development_dependency "minitest", "~> 5.14"
   s.add_development_dependency "pry-byebug"
   s.add_development_dependency "rake"
-  s.add_development_dependency "rubocop-govuk", "4.17.1"
+  s.add_development_dependency "rubocop-govuk", "4.18.0"
   s.add_development_dependency "simplecov"
 end