Restore "Add Gemfile.lock to the repo"

This reverts commit c0ecbca62509d3fe5ca60d2896c4e1be1444ae4c and restores commit
5ab43439a92e69fbfaddc09c670eb27eb8df623e.

I originally thought this was causing Travis to fail, but it looks to be
something else.
Extract list of targeted versions into a separate file
Target 2.0.0-p195 by default
Use 2.0.0-p195 instead of 2.0.0-p0
Turn on debugging when Travis runs tests