Add and enable rubocop-rake extension

.rubocop.yml

@@ -1,8 +1,11 @@
-require: rubocop-performance
+require:
+  - rubocop-performance
+  - rubocop-rake
 
 AllCops:
   Include:
     - 'lib/**/*'
+    - 'Rakefile'
   Exclude:
     - 'vendor/**/*'
     - 'benchmarks/*'

Rakefile

@@ -1,10 +1,12 @@
+# frozen_string_literal: true
+
 require 'bundler/setup'
 require 'rubygems/tasks'
 Gem::Tasks.new
 
 require 'rspec/core/rake_task'
 RSpec::Core::RakeTask.new(:spec) do |t|
-  t.rspec_opts = "--warnings"
+  t.rspec_opts = '--warnings'
 end
 
 require 'rubocop/rake_task'

colorls.gemspec

@@ -75,6 +75,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'rspec-its', '~> 1.2'
   spec.add_development_dependency 'rubocop', '~> 1.6.0'
   spec.add_development_dependency 'rubocop-performance', '~> 1.9.0'
+  spec.add_development_dependency 'rubocop-rake', '~> 0.5'
   spec.add_development_dependency 'rubocop-rspec', '~> 2.0'
   spec.add_development_dependency 'rubygems-tasks', '~> 0'
   spec.add_development_dependency 'simplecov', '~> 0.20.0'