Merge event approvals are in double-past tense

[totte]

Somewhere here things go awry: https://github.com/maubot/gitlab/blob/master/gitlab-webhook.go#L216

When I approve a merge request, the GitLab bot sends a notice like so:

[totte/foo] totte approveded merge request Initial commit (!1)

It should be as follows:

[totte/foo] totte approved merge request Initial commit (!1)