trouble pushing glimmerjs app to heroku?

I am trying to just host a basic toy glimmer.js app on heroku and followed the instructions below, but keep getting this error:

! [remote rejected] master -> master (pre-receive hook declined)

Any idea what might be going on here? Im in the root directory of my-app and on the master branch....

$ heroku create --buildpack http://ift.tt/2oiBVbe
    $ git push heroku master
    $ heroku open