Fix ruby_simple to support skinny buildpacks
Fix ruby_simple to support skinny buildpacks

* Upgrade gemfile to 2.1.6
[#94520922]

matt-royal/cf-acceptance-tests,matt-royal/cf-acceptance-tests,matt-royal/cf-acceptance-tests,matt-royal/cf-acceptance-tests,matt-royal/cf-acceptance-tests,matt-royal/cf-acceptance-tests,matt-royal/cf-acceptance-tests,matt-royal/cf-acceptance-tests