We use Fourchette (https://github.com/jipiboily/fourchette), which means we have a Heroku fork of our QA env for each GitHub PR.

Also, once something is on develop/staging, it is about to be shipped. If there is any bug in there, they are they should be fixed ASAP.

As we grow, we might have to do things differently, we'll see, but this works really well for us right now. :)