Add buildpack support to app.json for Heroku Button, GitHub Sync, Review Apps, and Dropbox Sync

Change effective on 24 June 2015

We’ve added a buildpacks field to app.json. Your Heroku Button apps can now specify more than one buildpack. To specify buildpacks, add an array of objects to your app.json:

{
  "buildpacks": [
    {
      "url": "https://github.com/heroku/heroku-buildpack-nodejs"
    },
    {
      "url": "https://github.com/heroku/heroku-buildpack-ruby"
    }
  ]
}

See the documentation for a complete example.