Choose a lower worker count
Add new relic gem

* Remove license key from the newrelic config file.

  Newrelic's configuration parser takes in configuration options from
  various sources, environment variables being one of them. In our case,
  the NewRelic addon adds a license key as a environment variable
  (NEW_RELIC_LICENSE_KEY) so this gets picked up without us committing
  the key to Git.
Try out Ruby 2.2.0!

* JSON gem installation fails with 2.2.0 but works with a patched
  version at `https://github.com/kgrz/json`