I was pushing the current git repository into the heroku. That online application was developed using Scala and IntelliJ. And I don\'t know how to fix this error.
You need to follow the instructions displayed here, on your case follow scala configuration:
https://devcenter.heroku.com/articles/getting-started-with-scala#introduction
After setting up the getting started pack, tweak around the default config and apply to your local repository. It should work, just like mine using NodeJS.
HTH! :)