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

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https://hg.mozilla.org/integration/gaia-central/rev/d1db45a074b9
Author: Mason Chang <mason@masonchang.com>
Desc: Merge pull request #16500 from changm/bug960325

Bug 960325 - Move Homescreen Background into Homescreen App. r=alive, crdlc

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https://hg.mozilla.org/integration/gaia-central/rev/a463921aeee5
Author: Mason Chang <mchang@mozilla.com>
Desc: Bug 960325 - Move Homescreen Background into Homescreen App. r=alive,
crdlc
Bumping manifests a=b2g-bump