Fix gemspec to not rely on git

This makes our deploys sad.

Change-Id: Ica81cfc53beac5132b9d79f9d470d9b6b4242581
Reviewed-on: https://gerrit.causes.com/18883
Reviewed-by: Greg Hurrell <greg@causes.com>
Tested-by: Aiden Scandella <aiden@causes.com>