Update omnibus gem's SHA in Gemfile.lock to latest commit in branch
The upstream branch of omnibus was updated in omnibus!9 (merged). This MR cherry-picks the changes made to omnibus-gitlab master to match with that change, to 11-8-stable-ee branch. Without this, there will be a mismatch in what Gemfile.lock shows and what upstream has, and builds will fail.
Edited by Balasankar 'Balu' C