When using git to deploy your app to Heroku, it is expected that you push
to the master branch. When you run the following command
$ git push heroku master
Heroku will attempt to build and run your app. However, if you have a
staging branch for your application that you want to push to your
staging environment on Heroku, you cannot simply run
$ git push heroku staging
Heroku will only perform a build on pushes to the remote master branch.
You can get around this, though, by specifying that your staging branch
should be pushed to the remote master branch, like so
$ git push heroku staging:master