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

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https://hg.mozilla.org/integration/gaia-central/rev/d9387352b54c
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #19799 from KevinGrandon/bug_1016233_collections_background

Bug 1016233 - [Collections] Background image sizing and overlay

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https://hg.mozilla.org/integration/gaia-central/rev/da21120b4b55
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 1016233 - [Collections] Background image sizing and overlay r=ranbena
Bumping manifests a=b2g-bump