Revert rubygems updates due to https://github.com/rubygems/rubygems/issues/3030
Revert rubygems updates due to https://github.com/rubygems/rubygems/issues/3030

[#170308120]

cloudfoundry/ruby-buildpack,cloudfoundry/ruby-buildpack,cloudfoundry/ruby-buildpack,cloudfoundry/ruby-buildpack,cloudfoundry/ruby-buildpack