Get rid of the deprecated appraisal rake tasks in favor of running
appraisal directly with `bundle exec appraisal rake`.
I also went ahead and updated all the gemfiles.
to run rubocop locally and not to wait for HoundCI to bark at us.
The version is locked to 0.54 because this is the version HoundCI is using.
Using a newer version will not work as config changed from 0.54 to currently 0.59
and rubocop would complain with the old configuration.
thoughtbot uses the .rubocop.yml in thoughtbot/guides
as the orginizational config on Hound, so we inherit
from it so we can use the same config locally.
Fix#1195.
