Support for user's permissions endpoint

[treeder]

Maybe I just can't find it, but it looks like this endpoint is not supported:

https://developer.github.com/v3/repos/collaborators/#review-a-users-permission-level

Was added fairly recently: https://developer.github.com/changes/2016-11-28-preview-org-membership/

[dmitshur]

I'm seeing it here:

https://godoc.org/github.com/google/go-github/github#RepositoriesService.GetPermissionLevel

Is that the one you're looking for?

We added it in #534.

[treeder]

That looks like the one, thanks!