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

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https://hg.mozilla.org/integration/gaia-central/rev/c6fff90a7657
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Merge pull request #22702 from AkshayTiwari/master

Bug 1006990 - Remove broken applicationCache handling in notification.js, r=timdream

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https://hg.mozilla.org/integration/gaia-central/rev/e985003c0351
Author: Akshay Tiwari <akshaytiwari.003@gmail.com>
Desc: Update notifications.js

Regarding the bug no. 1006990 .
Gaia apps was loaded with app cache, and we have switched to packaged app long time ago. However, there are still redundant code in the top of apps/system/js/notification.js on saving notification icons.
So removing the app cache code.
Bumping manifests a=b2g-bump