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

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https://hg.mozilla.org/integration/gaia-central/rev/8dfeb9483a36
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #14205 from bebef1987/prefs

Bug 942909 - Add in the gaia test cleanUp() a option to setup prefs

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https://hg.mozilla.org/integration/gaia-central/rev/db575d9580c1
Author: Bebe <bebe@mozilla.ro>
Desc: Bug 942909 - Add in the gaia test cleanUp() a option to setup prefs r=davehunt bsilvergberg
Bumping manifests a=b2g-bump