create merge request throws 404 when requests already exists

[logicminds]

When creating a merge request the first attempt works great. However, if someone tries to create the same merge request again, a 404 error is throw. Either this is the gitlab api issue or this gem needs to handle this response better (304 maybe). Either way this gem should not throw an error on additional create_request attempts.

[NARKOZ]

It's the way how GitLab API handles errors.

https://github.com/gitlabhq/gitlabhq/issues/5335
https://github.com/gitlabhq/gitlabhq/issues/6878