Your worker is actually pretty ineffective, there are better solutions that give you hashrate about 110 h/s, but don't try to do that. Mining cryptocurrencies is prohibited on Heroku https://www.heroku.com/policy/aup and they will suspend your account.
(sorry is should be comment to author of this tutorial, not to you @amatiash)
...And then I witnessed this almost the same comment... ;)
I want to apologize to you both. I don't know what I was thinking and never bothered to look at the terms and conditions. I was lucky not to have my account suspended. Heroku is a great service.