Bumping gaia.json for 2 gaia revision(s) a=gaia-bump

========

https://hg.mozilla.org/integration/gaia-central/rev/ef21987c1201
Author: Sherman Chen <shamenchens@users.noreply.github.com>
Desc: Merge pull request #23550 from shamenchens/Bug1059748-GalleryPreview-Part1

Bug 1058748 - Fix gallery preview on tablet, r=dflanagan

========

https://hg.mozilla.org/integration/gaia-central/rev/33dc2dc313f2
Author: Sherman Chen <shamen.chens@gmail.com>
Desc: Bug 1059748 - Fix gallery preview on tablet
Bumping manifests a=b2g-bump