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

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https://hg.mozilla.org/integration/gaia-central/rev/c31adc354aab
Author: Arthur Chen <crh0716@gmail.com>
Desc: Merge pull request #19054 from crh0716/973453

Bug 973453 - Separate root panel r=evelyn

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https://hg.mozilla.org/integration/gaia-central/rev/cc0b13e1c21f
Author: Arthur Chen <crh0716@gmail.com>
Desc: Bug 973453 - Separate root panel
Bumping manifests a=b2g-bump