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

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https://hg.mozilla.org/integration/gaia-central/rev/753b73577392
Author: Vivien Nicolas <21@vingtetun.org>
Desc: Bug 964173 - [Messages] Remove the css animation 'peek' hack r=julien
Bumping manifests a=b2g-bump