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

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https://hg.mozilla.org/integration/gaia-central/rev/da96459c3d27
Author: Evelyn Eastmond <evhan55@gmail.com>
Desc: Bug 959696 - [Messages][Drafts][Refactoring] Move draft saving on visibility change to ThreadUI, and only store drafts if new one is saved r=rwaldron
Bumping manifests a=b2g-bump