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

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https://hg.mozilla.org/integration/gaia-central/rev/77ac5306cad9
Author: Ben Kelly <bkelly@mozilla.com>
Desc: Merge pull request #12919 from wanderview/contacts-duplicate-tests

Bug 927877: Check if img is already loaded.  r=arcturus

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https://hg.mozilla.org/integration/gaia-central/rev/12135a94b83f
Author: Ben Kelly <ben@wanderview.com>
Desc: Bug 927877: Check if img is already loaded.