Add ruby 2.6.7, remove ruby 2.6.5
Add ruby 2.6.7, remove ruby 2.6.5

for stack(s) cflinuxfs3 [#177625006]

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