update Gemfile rspec-puppet to point to upstream git

The patch needed to properly test the port389_nssd_add_cert() function
has been merged:

https://github.com/rodjek/rspec-puppet/pull/155
https://github.com/rodjek/rspec-puppet/commit/03e94422fb9bbdd950d5a0bec6ead5d76e06616b