On a pretty small instance (1.7g ram google cloud) + 1gb disk swap the omninbus update failed with out of memory. Added some more swap space and it finished fine. It's probably not powerful enough to run it though.. Just a heads up.
I'm sorry to hear that. We advise a minimum of 2gb of ram, so I'd expect it run successful for you. I created an issue on the omnibus issue tracker about the memory requirement for upgrades, here: https://gitlab.com/gitlab-org/omnibus-gitlab/issues/1135
