Avoid Ruby versions check on Rubinius

Rubinius is still targeting compliance with Ruby 2.1.0 but we are pretty
close to a green build so let's avoid this check for the moment.

railties/lib/rails/ruby_version_check.rb

-if RUBY_VERSION < '2.2.0'
+if RUBY_VERSION < '2.2.0' && RUBY_ENGINE == 'ruby'
   desc = defined?(RUBY_DESCRIPTION) ? RUBY_DESCRIPTION : "ruby #{RUBY_VERSION} (#{RUBY_RELEASE_DATE})"
   abort <<-end_message