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

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https://hg.mozilla.org/integration/gaia-central/rev/cb373c5f1a1a
Author: Fabien Cazenave <fabien@mozilla.com>
Desc: Merge pull request #15212 from 6a68/bug-950821-presetpanel-comment-fix

Bug 950821 - Add comment clarifying 'undefined' check, r=kaze

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https://hg.mozilla.org/integration/gaia-central/rev/5e81c34f2fa9
Author: Jared Hirsch <ohai@6a68.net>
Desc: Bug 950821 - Add comment clarifying 'undefined' check
Bumping manifests a=b2g-bump