Correct docs that mirror push is in Core (!19518) · Merge requests · GitLab.org / GitLab FOSS · GitLab

Achilleas Pipinellis - OOO until November 25th (parental leave) requested to merge docs/push-remote-repo-core into master Jun 07, 2018

What does this MR do?

Mirror push was moved to Core in 10.8. check https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/18715