downgrade psych

Author: tenderlove

Gemfile

@@ -17,7 +17,7 @@ group :test do
   gem 'rspec', '~> 3.2'
 
   # Downgrade psych because old RuboCop can't use new Psych
-  gem 'psych', '~> 3.3.2'
+  gem 'psych', '< 4.0.0'
   # https://github.com/bbatsov/rubocop/pull/4789
   gem 'rubocop', '~> 0.50.0'
 end