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

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https://hg.mozilla.org/integration/gaia-central/rev/30916a0e4fa2
Author: Evelyn Eastmond <evhan55@gmail.com>
Desc: Bug 964862 - [Messages][Drafts][Refactoring] Move MessageManager.draft to ThreadUI.draft
Bumping manifests a=b2g-bump