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

========

https://hg.mozilla.org/integration/gaia-central/rev/4e61c55c586b
Author: Jared Hirsch <ohai@6a68.net>
Desc: Merge pull request #19792 from 6a68/bug-1011498-scale-fxa-bkgd-imgs

Bug 1011498 - Force FxA background images to scale to different resolution screens

========

https://hg.mozilla.org/integration/gaia-central/rev/72b2d3b1afc7
Author: Jared Hirsch <ohai@6a68.net>
Desc: Bug 1011498 - Force FxA background images to scale to different resolution screens. r=ferjm,arthurcc
Bumping manifests a=b2g-bump