Fix for error in gitlab_ci init script

Hi,
I followed this great installation instruction:

https://github.com/gitlabhq/gitlab-ci/blob/master/doc/installation.md

and I noticed that there is bug in gitlab_ci init script. It wasn't able to start the GitLab CI service, because options and parameters of `puma` were interpreted as options and parameters of `bundle exec`. This pull request fixes this bug.

Jiri