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

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https://hg.mozilla.org/integration/gaia-central/rev/a015b356e984
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #21143 from KevinGrandon/bug_1028688_collection_pinned_push_to_unshift

Bug 1028688 - [Collection] Render icon after an add operation from homescreen

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https://hg.mozilla.org/integration/gaia-central/rev/bb6f2e8c7113
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 1028688 - [Collection] Render icon after an add operation from homescreen r=ranbena
Bumping manifests a=b2g-bump