Developer credits

Git commits in Moodle 3.9.0 by John Yao

commit 978570637dad521132381e31a6941f95401e771b
Author: John Yao <johnyao@catalyst-au.net>
Date:   Mon, 16 Dec 2019 08:28:04 +0800
Tag:    v3.9.0-beta

MDL-67524 book: fixing view hidden chapter issue

commit 9514c1ac35edfdbe938ea2c14545b79a3d5c2e60
Author: John Yao <johnyao@catalyst-au.net>
Date:   Fri, 06 Dec 2019 10:46:21 +0800
Tag:    v3.9.0-beta

MDL-67467 Reports: sortable date format in pregress csv report

commit d0734df40426c40eae9bde0cc41c08b43560962b
Author: John Yao <johnyao@catalyst-au.net>
Date:   Tue, 06 Aug 2019 10:49:35 +0800
Tag:    v3.9.0-beta

MDL-65729 Backup: Split individual backups into ad-hoc tasks