In order to deploy to heroku, you'll need to run this command once to set a custom buildpack:
heroku config:add BUILDPACK_URL=https://github.com/ddollar/heroku-buildpack-multi.git
This runs the two buildpacks in the .buildpacks directory.
Also make sure you are running the latest heroku stack, cedar-14, to avoid running into the following issue.
heroku stack:set cedar-14 -a react-webpack-rails-tutorial
To deploy the app on Heroku:
git push heroku master