Remove Gemfile.lock from repo

Gems aren't supposed to include a `Gemfile.lock` since the Gemspec
should explicitly list all dependencies.

Change-Id: I9f1f90179994337a5283cfa27d7e3ace4f0851e2
Reviewed-on: https://gerrit.causes.com/30173
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>