Bumping gaia.json for 2 gaia-1_3 revision(s) a=gaia-bump

========

https://hg.mozilla.org/integration/gaia-1_3/rev/f18ae8ca1f1f
Author: Alive.Kuo <alegnadise@gmail.com>
Desc: Merge pull request #15674 from alivedise/bugzilla/961569_v1.3/fullscreen-modal-dialog

Bug 961569 - Fix modal dialog under mozfullscreen, r=timdream, a=1.3+

========

https://hg.mozilla.org/integration/gaia-1_3/rev/767956e21146
Author: Alive Kuo <alegnadise@gmail.com>
Desc: Bug 961569 - Fix modal dialog under mozfullscreen

Conflicts:
	apps/system/style/window.css