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

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https://hg.mozilla.org/integration/gaia-central/rev/debbe27e7bc3
Author: Joan Leon <joan.leon@gmail.com>
Desc: Bug 963018 - [Messages][Refresh] Update styles of the Composer r=julien
Bumping manifests a=b2g-bump