Bumping gaia.json for 1 gaia-central revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/4b7abda13eec
Author: Evelyn Eastmond <evhan55@gmail.com>
Desc: Bug 947217 - [Messages][Drafts] Consider removing the 'Drafts.request()' call in MessageManager's init r=rwaldron