I consolidated all the development dependencies in the gemspec,
then ran `bundle update` and `appraisal install`.
I also got rid of unnecessary version constraints (I would rather just
the latest versions of things in development, and we can always add
constraints later if necessary), and removed the jruby-specific gems
since we aren't testing on jruby anymore.
With `git ls-files` we were still including unneeded dotfiles and
appraisal files. This switches to a whitelist of files included in the
gem, rather than a blacklist. I also tried to make RuboCop happy while I
was in here.
Daniel Colson