Add ruby 2.4.6, remove ruby 2.4.4
Add ruby 2.4.6, remove ruby 2.4.4

for stack(s) cflinuxfs2, cflinuxfs3 [#165037294]

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