Add rubocop-performance

This feature was moved from rubocop to this gem.

.rubocop.yml

@@ -1,3 +1,5 @@
+require: rubocop-performance
+
 # Stolen from https://gist.github.com/jhass/a5ae80d87f18e53e7b56
 AllCops:
   Exclude:

Gemfile

@@ -57,6 +57,7 @@ group :development do
   # Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
   gem 'railroady'
   gem 'rubocop'
+  gem 'rubocop-performance'
   gem 'solargraph'
   gem 'spring'
   gem 'spring-watcher-listen', '~> 2.0.0'

Gemfile.lock

@@ -202,6 +202,8 @@ GEM
       rainbow (>= 2.2.2, < 4.0)
       ruby-progressbar (~> 1.7)
       unicode-display_width (>= 1.4.0, < 1.6)
+    rubocop-performance (1.2.0)
+      rubocop (>= 0.68.0)
     ruby-progressbar (1.10.0)
     ruby_dep (1.5.0)
     shoulda-matchers (4.0.1)
@@ -278,6 +280,7 @@ DEPENDENCIES
   rails (~> 5.2.1)
   rspec-rails
   rubocop
+  rubocop-performance
   shoulda-matchers
   solargraph
   spring