Update Mattermost to 5.2.2 (GitLab 11.3)
Mattermost 5.2.2 is a regular security release for an S2 issue that has also been fixed in 5.3.0 and 5.1.2
Mattermost 5.2.2 is a regular security release for an S2 issue that has also been fixed in 5.3.0 and 5.1.2