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

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https://hg.mozilla.org/integration/gaia-central/rev/47260e362bbd
Author: Ben Kelly <bkelly@mozilla.com>
Desc: Merge pull request #12673 from wanderview/contacts-dynamic-group

Bug 921683: defer contact group DOM creation. r=jmcf

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https://hg.mozilla.org/integration/gaia-central/rev/3c1f3b0f4d2c
Author: Ben Kelly <ben@wanderview.com>
Desc: Bug 921683: defer contact group DOM creation