See virtualstaticvoid/heroku-buildpack-r#107
heroku create --stack heroku-16
heroku buildpacks:add https://github.com/virtualstaticvoid/heroku-buildpack-r.git#heroku-16
git push heroku master
heroku logs # to check
curl -v -L https://your-heroku-app-name.heroku.com/mean
curl -v -d "a=1" -d "b=2" -L https://your-heroku-app-name.herokuapp.com/sum