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

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https://hg.mozilla.org/integration/gaia-central/rev/0687fc8babad
Author: Fabrice Desré <fabrice@desre.org>
Desc: Merge pull request #12799 from cvan/updated-mkt

Bug 925804 - Update Marketplace for webactivities+e.me

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https://hg.mozilla.org/integration/gaia-central/rev/14e54ebb6660
Author: Chris Van <cvan@mozilla.com>
Desc: Bug 925804 - Update Marketplace for webactivities+e.me. r=fabrice