Make detection of services team case-insensitive

* Update `GithubApi#find_team` to detect existing services team with
  lowercase name
* Addresses https://github.com/thoughtbot/hound/issues/454
* https://trello.com/c/q9z4wV19/398-activation-fails-when-repo-belongs-to-organization-with-services-lowercase-team
Update repo name when receiving PR payload

This will prevent us from getting out of sync repo names, which causes
an issue when we try to process the PR, since our and GitHub repo names
are mismatched.