Switch to indented access modifiers style

This style seems to have won favor in the general community. Switch to
it.

Change-Id: I739c914adbbb6db2380c287872cf10b308275e43
Reviewed-on: http://gerrit.causes.com/42557
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>
Upgrade Travis build RuboCop from 0.25.0 -> 0.26.0

For the purposes of linting `haml-lint` itself, upgrade to the latest
RuboCop version.

Change-Id: I75e83591a670608b5c5cd07446e245d6339e6aa6
Reviewed-on: http://gerrit.causes.com/42558
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>