Merge pull request #392 from oauth-xx/depfu/update/rubocop-0.57.2

Upgrade rubocop to version 0.57.2

Author: pboling

Gemfile

@@ -5,7 +5,7 @@ git_source(:github) { |repo_name| "https://github.com/#{repo_name}" }
 group :test do
   ruby_version = Gem::Version.new(RUBY_VERSION)
   if ruby_version >= Gem::Version.new('2.1')
-    gem 'rubocop', '~> 0.56.0'
+    gem 'rubocop', '~> 0.57.2'
     gem 'rubocop-rspec', '~> 1.27.0'
   end
   gem 'pry', '~> 0.11' if ruby_version >= Gem::Version.new('2.0')