Our current unicorn task wasn't working in some cases. We also had a
version in the `capistrano` branch, which was the one we recommended.
However, that version assumed RVM, a certain ruby version and a certain
deploy folder were used. This version uses `bundle exec` and variables
like `release_path`, so it does not depend on any specific
configuration.
Even if we're replacing unicorn with puma, I wanted to make this change
in case we need it as a reference in the future.
94a7e13dce