Update traefik dependencies (docker/docker and related) (#1823)

Update traefik dependencies (docker/docker and related)

- Update dependencies
- Fix compilation problems
- Remove vdemeester/docker-events (in docker api now)
- Remove `integration/vendor`
- Use `testImport`
- update some deps.
- regenerate the lock from scratch (after a `glide cc`)

vendor/github.com/google/go-github/github/repos_invitations.go

@@ -90,5 +90,9 @@ func (s *RepositoriesService) UpdateInvitation(ctx context.Context, owner, repo
 
 	invite := &RepositoryInvitation{}
 	resp, err := s.client.Do(ctx, req, invite)
-	return invite, resp, err
+	if err != nil {
+		return nil, resp, err
+	}
+
+	return invite, resp, nil
 }