Git merges in Moodle 3.1.18 by Eloy Lafuente (stronk7)

commit 5561a23dad72c853fb669f3963bf7d2a5cfd960a
Author: Eloy Lafuente (stronk7) <stronk7@moodle.org>
Date:   Sat, 11 May 2019 02:30:57 +0800
Tag:    v3.1.18

Merge branch 'install_31_STABLE' of https://git.in.moodle.com/amosbot/moodle-install into MOODLE_31_STABLE