https://github.com/puma/puma-dev needs the puma gem added to your Gemfile in order for the app to boot.
If you are using rvm
and https://gist.github.com/Chocksy/a00307aabfe96b684b92d5ffd471e3e7 to add your own gems and puma is added there then you need to add some changes to .powconfig
so it loads the gems from the local file first.