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

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https://hg.mozilla.org/integration/gaia-1_3/rev/15b5e8c65cc4
Author: Gabriele Svelto <gsvelto@mozilla.com>
Desc: Bug 981521 - Display notifications for messages with a "signal-none" action r=julienw

Conflicts:
	apps/wappush/js/wappush.js
Bumping manifests a=b2g-bump