Somehow I completely failed at copying code [from StackOverflow](https://speakerdeck.com/noelrap/the-road-to-legacy-is-paved-with-good-intentions) in https://github.com/pelias/api/pull/983. Instead of skipping Docker image builds only for branches with greenkeeper in the name, it _always_ skipped the build! Connects https://github.com/pelias/dockerfiles/issues/21