Add rubocop-rails gem

The rails cops used to be in the rubocop gem itself but moved into their
own gem recently. Our style guide refers to these cops though.

.rubocop.yml

@@ -4,6 +4,7 @@
 #
 # The configuration is split into three files. Look into those files for more details.
 #
+require: rubocop-rails
 inherit_from:
 
   # The automatically generated todo list to ignore all current violations.

Gemfile

@@ -163,7 +163,8 @@ group :development do
   gem 'debugger-linecache'
   gem "newrelic_rpm", "~> 3.0"
   gem 'pry-byebug', '>= 3.4.3'
-  gem 'rubocop', '>= 0.49.1'
+  gem 'rubocop'
+  gem 'rubocop-rails'
   gem 'spring', '1.7.2'
   gem 'spring-commands-rspec'
 

Gemfile.lock

@@ -621,6 +621,9 @@ GEM
       rainbow (>= 2.2.2, < 4.0)
       ruby-progressbar (~> 1.7)
       unicode-display_width (>= 1.4.0, < 1.7)
+    rubocop-rails (2.4.1)
+      rack (>= 1.1)
+      rubocop (>= 0.72.0)
     ruby-ole (1.2.12.1)
     ruby-progressbar (1.10.1)
     ruby-rc4 (0.1.5)
@@ -792,7 +795,8 @@ DEPENDENCIES
   roo-xls (~> 1.1.0)
   rspec-rails (>= 3.5.2)
   rspec-retry
-  rubocop (>= 0.49.1)
+  rubocop
+  rubocop-rails
   sass (~> 3.3)
   sass-rails (~> 3.2.3)
   selenium-webdriver