remove Gemfile.lock from gem

[thomasdziedzic-calmwave]

our vulnerability scanner is picking this file up and marking it as a false positive because there's a vulnerable version of nokogiri in there, I think there doesn't need to be a Gemfile.lock at all in the gem.

[Skulli]

It is common to include the lock file into the ruby repository. In this case the gem just needs an update.