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

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https://hg.mozilla.org/integration/gaia-central/rev/b61881379455
Author: kumarrishav <rishav006@gmail.com>
Desc: Bug 926385 - [Messages] saner button css rules r=julien,schung
Bumping manifests a=b2g-bump