Git commits in Moodle 3.6.0 by Claude Vervoort

commit 29acede1f08150ddf3953faa13b9e82701f84c1e
Author: Claude Vervoort <claude.vervoort@cengage.com>
Date:   Thu, 26 Jul 2018 23:20:04 +0800
Tag:    v3.6.0-beta

MDL-62993 ltiservice_memberships: make message an array per spec