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

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https://hg.mozilla.org/integration/gaia-central/rev/47e88e2fccb1
Author: Gonzalo Martinez <gmartinez@panareadigital.com>
Desc: Bug 1028190 - Allow MockContact properties to be None
Bumping manifests a=b2g-bump