Add rubocop to our build. (#5004)

config/initializers/099-anon-cache.rb

@@ -1,13 +1,13 @@
 require_dependency "middleware/anonymous_cache"
 
-enabled = if Rails.configuration.respond_to?(:enable_anon_caching)
-            Rails.configuration.enable_anon_caching
-          else
-            Rails.env.production?
-          end
+enabled =
+  if Rails.configuration.respond_to?(:enable_anon_caching)
+    Rails.configuration.enable_anon_caching
+  else
+    Rails.env.production?
+  end
 
 if !ENV['DISCOURSE_DISABLE_ANON_CACHE'] && enabled
   # in an ideal world this is position 0, but mobile detection uses ... session and request and params
   Rails.configuration.middleware.insert_after ActionDispatch::ParamsParser, Middleware::AnonymousCache
 end
-