Gemfile in uglifier-3.2.0 vs Gemfile in uglifier-4.0.0

@@ -1,5 +1,5 @@
 source "https://rubygems.org"
 
 gemspec
 
-gem 'rubocop', '~> 0.48.0', :group => [:development] if RUBY_VERSION >= '2.0'
+gem 'rubocop', '~> 0.51.0', :group => [:development] if RUBY_VERSION >= '2.1'