Introduces rubocop-performance

.rubocop.yml

@@ -2,6 +2,7 @@ require:
   - rubocop-rspec
   - rubocop-rails
   - rubocop-capybara
+  - rubocop-performance
 
 inherit_from: .rubocop_todo.yml
 

Gemfile

@@ -236,6 +236,7 @@ group :development do
   gem 'rubocop-rspec', require: false
   gem 'rubocop-rails', require: false
   gem 'rubocop-capybara', require: false
+  gem 'rubocop-performance', require: false
   gem 'haml_lint'
   # to open mails
   gem 'letter_opener'

Gemfile.lock

@@ -509,6 +509,9 @@ GEM
       parser (>= 3.2.1.0)
     rubocop-capybara (2.18.0)
       rubocop (~> 1.41)
+    rubocop-performance (1.17.1)
+      rubocop (>= 1.7.0, < 2.0)
+      rubocop-ast (>= 0.4.0)
     rubocop-rails (2.15.0)
       activesupport (>= 4.2.0)
       rack (>= 1.1)
@@ -719,6 +722,7 @@ DEPENDENCIES
   rspec-rails
   rubocop
   rubocop-capybara
+  rubocop-performance
   rubocop-rails
   rubocop-rspec
   ruby-oembed