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

========

https://hg.mozilla.org/integration/gaia-central/rev/b2c161079091
Author: Andrew Sutherland <asutherland@asutherland.org>
Desc: Merge pull request #13540 from asutherland/makefile-fix

Bug 931550 - Clock and Mail app only have rocket icon on homescreen, can't launch/broken. r=:yurenju

========

https://hg.mozilla.org/integration/gaia-central/rev/ad1506647118
Author: Andrew Sutherland <asutherland@asutherland.org>
Desc: Bug 931550 - Clock and Mail app only have rocket icon on homescreen, can't launch/broken