Fix psych, close #2823

Author: nateberkopec

Gemfile

@@ -14,6 +14,7 @@ gem "minitest-proveit"
 gem "jruby-openssl", :platform => "jruby"
 
 gem "rubocop", "~> 0.58.0"
+gem "psych", "~> 3.0"
 
 if %w(2.2.7 2.2.8 2.2.9 2.2.10 2.3.4 2.4.1).include? RUBY_VERSION
   gem "stopgap_13632", "~> 1.0", :platforms => ["mri", "mingw", "x64_mingw"]