Remove Gemfile.lock

Gems should enforce dependencies in the gemspec rather than via a
`Gemfile.lock` file.

Change-Id: Ib4599c390125a8b519f86b25e3f8b73953db6130
Reviewed-on: https://gerrit.causes.com/30955
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>