Add bundler 2.3.7, remove bundler 2.3.6
Add bundler 2.3.7, remove bundler 2.3.6

for stack(s) cflinuxfs3 [#181206615]

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