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

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https://hg.mozilla.org/integration/gaia-central/rev/c97a6a8850ae
Author: Ben Kelly <bkelly@mozilla.com>
Desc: Merge pull request #13043 from wanderview/contacts-size-reflow

Bug 921685: Read device geometry info from cookie to avoid sync reflows. r=arcturus

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https://hg.mozilla.org/integration/gaia-central/rev/1a35f8059551
Author: Ben Kelly <ben@wanderview.com>
Desc: Bug 921685: Read device geometry info from cookie to avoid sync reflows.