Heroku Cedar-14

Heroku recently upgraded their default deployment stack called
“Cedar-14”. To use this upgraded stack, you need to make a change to the
project template (note, you won’t hit any issues until you try to deploy
on Heroku):

    Add a new file to the project called Procfile. In this file, add the
line: web: bundle exec ruby main.rb -p $PORT

The Procfile should be capitalized, no extension and be in the root of
the Sintra app (peer to the Gemfile file).