This is basically a bastardized fork of the heroku-buildpack-ruby buildpack that will just setup ruby, bundle install and run a rake task.
It's currently hardcoded for i18n:js:export; if you want to change that look in ruby.rb:107 as a starting point.
There is a generic
run_rake_task(name) method that you can use to run whatever task (or multiple)
you would like.
Copy the snippet above into CLI.