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

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https://hg.mozilla.org/integration/gaia-central/rev/21b08b5edd90
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #22642 from KevinGrandon/bug_1050339_collection_icons

Bug 1050339 - [B2G][Smart Collections] Default Smart Collections are missing their icons

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https://hg.mozilla.org/integration/gaia-central/rev/3624c1f1bcbd
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 1050339 - [B2G][Smart Collections] Default Smart Collections are missing their icons r=yurenju
Bumping manifests a=b2g-bump