Using rubocop rails gem

.rubocop.yml

-require: rubocop-performance
+require:
+  - rubocop-performance
+  - rubocop-rails
 
 AllCops:
   Exclude:

Guardfile

@@ -34,7 +34,7 @@ guard :brakeman, run_on_start: true, quiet: true, min_confidence: 10 do
   watch('Gemfile')
 end
 
-guard :rubocop, cli: ['--rails'] do
+guard :rubocop do
   watch(%r{.+\.rb$})
   watch(%r{(?:.+/)?\.rubocop\.yml$}) { |m| File.dirname(m[0]) }
 end