Add rubocop to our build. (#5004)

lib/middleware/missing_avatars.rb

@@ -5,19 +5,19 @@ module Middleware
   # due to the files not being present locally. This middleware, only enabled in development
   # mode, will replace those with an appropriate image.
   class MissingAvatars
-    def initialize(app, settings={})
+    def initialize(app, settings = {})
       @app = app
     end
 
     def call(env)
       if (env['REQUEST_PATH'] =~ /^\/uploads\/default\/avatars/)
         path = "#{Rails.root}/public#{env['REQUEST_PATH']}"
-        unless File.exist?(path) 
+        unless File.exist?(path)
           default_image = "#{Rails.root}/public/images/d-logo-sketch-small.png"
           return [ 200, { 'Content-Type' => 'image/png' }, [ File.read(default_image)] ]
         end
       end
-      
+
       status, headers, response = @app.call(env)
       [status, headers, response]
     end