More Rubocop!

See https://github.com/neo4jrb/neo4j/pull/652

Also for reference:

Master:
[![PullReview stats](https://www.pullreview.com/github/neo4jrb/neo4j-core/badges/master.svg?)](https://www.pullreview.com/github/neo4jrb/neo4j-core/reviews/master)

This branch:
[![PullReview stats](https://www.pullreview.com/github/neo4jrb/neo4j-core/badges/rubocop.svg?)](https://www.pullreview.com/github/neo4jrb/neo4j-core/reviews/rubocop)