Add rubygems 3.0.4, remove rubygems 3.0.3
Add rubygems 3.0.4, remove rubygems 3.0.3

for stack(s) cflinuxfs2, cflinuxfs3 [#166692324]

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