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

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https://hg.mozilla.org/integration/gaia-central/rev/4d927569e6eb
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #15153 from davehunt/bug_946711

Bug 946711 - Run Travis-CI scripts in a virtual environment

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https://hg.mozilla.org/integration/gaia-central/rev/4011ba49893a
Author: Dave Hunt <dave.hunt@gmail.com>
Desc: Bug 946711 - Run Travis-CI scripts in a virtual environment. r=zcampbell