Remove Gemfile.lock

We shouldn't be commiting the `Gemfile.lock` file in the repository.
Instead, the gemspec should specify all necessary dependencies.

Change-Id: I1ff83ed955744f44fdf8002e41ec3da66f4d218a
Reviewed-on: https://gerrit.causes.com/29921
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>