Add rubygems 3.2.0, remove rubygems 3.1.5
Add rubygems 3.2.0, remove rubygems 3.1.5

for stack(s) cflinuxfs3 [#176088849]

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