ListProjectContributionEvents fails with 404 error

Created by: 7fELF

EventsService.ListProjectContributionEvents is failing with a 404 error.

The function is calling https://gitlab.com/api/v4/000000/events instead of https://gitlab.com/api/v4/projects/0000000/events

I can fix it by adding projects/ in the Sprintf here: https://github.com/xanzy/go-gitlab/blob/af28ecc530599f542dee9a748c4a8e3a22ae4659/events.go#L133

Did I miss something or is this really a bug ?