Bumping gaia.json for 1 gaia revision(s) a=gaia-bump

========

https://hg.mozilla.org/integration/gaia-1_3/rev/843f122cd5ef
Author: Amir Nissim <amirnissim@gmail.com>
Desc: Merge pull request #16570 from EverythingMe/973864-set-wallpaper

Bug 973864 - [Everything.me] Set Collection background image as wallpape...
Bumping manifests a=b2g-bump