Upgrade Rubocop to 0.23.0

We're now checking style using the latest Rubocop.

Change-Id: I9d231ead9d4ce95a178c31ed79d9333f449e0da0
Reviewed-on: http://gerrit.causes.com/38494
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>