Heroku's standard tier doesn't have auto-scaling. You have to be using the $250/month performance dynos for it. I'd suspect that's not feasible for a little hobby project.
I did not expect it to get any attention, so it was on the free tier dyno when it hit the front page. (And even seem to have held up for some time judging by the logs, before dying from the extreme lack of available ram.) Bumping it to the standard dyno when I noticed the issue was enough to keep it running.
