Update Mattermost to 5.1.2 (GitLab 11.2)
Mattermost 5.1.2 is a regular security release for an S2 issue that has also been fixed in 5.2.2 and 5.3.0
Mattermost 5.1.2 is a regular security release for an S2 issue that has also been fixed in 5.2.2 and 5.3.0