Fix Rubocop offenses

[weppos]

I upgraded Rubocop, and run it. There's several offenses that could be auto-corrected. And more that instead will need manual correction.

It's based on top of https://github.com/floere/phony/pull/557, will rebase once https://github.com/floere/phony/pull/557 is merged, and address the remaining cops.