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

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https://hg.mozilla.org/integration/gaia-central/rev/d49bbb7939a6
Author: Arthur Chen <crh0716@gmail.com>
Desc: Merge pull request #16108 from gurumukhi/master

Bug 910648 - Enable USB Storage should have one r=crh0716

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https://hg.mozilla.org/integration/gaia-central/rev/f893d0263b9c
Author: Ram Dayal Vaishnav <vaishnav.rd@gmail.com>
Desc: Bug 910648 - Enable USB Storage should have one
Bumping manifests a=b2g-bump