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

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https://hg.mozilla.org/integration/gaia-central/rev/975290b6ab3c
Author: Julien Wajsberg <felash@gmail.com>
Desc: Bug 1090945 - [Messages] icon for an "email" recipient is too big on Flame r=asazypkin

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https://hg.mozilla.org/integration/gaia-central/rev/d7b5f0c8ffee
Author: Julien Wajsberg <felash@gmail.com>
Desc: Bug 1076729 - [MMS]it is not scrolled to the most recent message r=schung
Bumping manifests a=b2g-bump