Bumping gaia.json for 1 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/3d4209fdf720
Author: Dave Hunt <dave.hunt@gmail.com>
Desc: Bug 909839 - Merge JavaScript 'atoms' used by gaia and gaiatest. r=jgriffin r=zcampbell
Bumping manifests a=b2g-bump