Include GitLab merge requests in lita pr list command

- Added fixture for web hook from gitlab
- Added endpoint to listen for merge request events
- Merge requests in 'opened' state get inserted into redis, otherwise
  they get removed. Don't know the other states, or what payload looks
like when a MR is closed.
- Converted Github PR list to return an array of PR messages, to make it
  easier to combine with the new GitLab MR list.
- Need more tests.
Added tests, made them pass
Don't need octokit
Bumping gem version... for some reason it's in its own file
Used full names to be less confusing for Pull Requests and Merge Requests.
Merged in master
Merge pull request #24 from amaabca/gitlab-webhook

Gitlab webhook