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

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https://hg.mozilla.org/integration/gaia-central/rev/cfcc2503c97b
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Merge pull request #15716 from timdream/background-color

Bug 948208 - Add black background on body before loadend, r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/9353926a97ff
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Bug 948208 - Add black background on body before loadend
Bumping manifests a=b2g-bump