Updated the code for Ruby 1.8.7 compatibility

This pull request is for [issue #19](https://github.com/gitlabhq/gitlab-ci-runner/issues/19)

I have tested it with `ree-1.8.7-2012.02`.


Maybe this pull request could be rejected in order to merge it in a separated branch than `master` and updating the documentation in order to inform people to `checkout` the right branch if they use ruby 1.8.