Heroku Buildpack for Ghostscript

# Use heroku-buildpack-multi
$ cd /path/to/your-app
$ heroku config:add BUILDPACK_URL=https://github.com/ddollar/heroku-buildpack-multi.git

# Create a .buildpacks file with including ghostscript
$ cd /path/to/your-app
$ cat .buildpacks
https://github.com/heroku/heroku-buildpack-ruby.git
https://github.com/bvirlet/heroku-buildpack-ghostscript.git

# Push changes to deploy
$ git push