Remove dead code from Gemfile
Use HTTPS connection to RubyGems
Remove autotest gem

We already have guard installed, and autotest gave me the following error while
bundle installing.

> Gem::InstallError: ZenTest requires RubyGems version < 2.1, >= 1.8. Try 'gem
> update --system' to update RubyGems itself.
> An error occurred while installing ZenTest (4.9.1), and Bundler cannot continue.
> Make sure that `gem install ZenTest -v '4.9.1'` succeeds before bundling.