Update git vendor to gitlab
Update git vendor to gitlab

Now that we are using gitaly to compile git, the git version isn't known
from the manifest, instead we are getting the gitaly version. Update our
vendor field to be `gitlab` to avoid cve matching old versions.

Changelog: changed

gitlabhq/omnibus-gitlab,gitlabhq/omnibus-gitlab,gitlabhq/omnibus-gitlab,gitlabhq/omnibus-gitlab