Support style-guide only usage

Many cops that have been implemented and enabled by default have no
correlation to a style-guide rule: `Metrics/ClassLength`,
`Metrics/AbcSize`, `Metrics/PerceivedComplexity` just to name a few. In
cases where these cops find violations, there's little recourse as the
rules cannot be traced back to a meaningful discussion or consensus.

The `--only-guide-cops` and `AllCops/StyleGuideCopsOnly` options give
users an easy method of invoking RuboCop in a way that's more congruent
with the rules of the style guide.
Ah, got it. Will do. That's still seems strange considering the trailing conditionals above it are semantically equivalent, yet they didn't trigger a violation. Is this maybe a false-positive bug in `GuardClause`?