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

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https://hg.mozilla.org/integration/gaia-central/rev/d19c27fb6208
Author: James Lal <james@lightsofapollo.com>
Desc: Merge pull request #12777 from lightsofapollo/more-recent-b2g

Bug 919882 - Use latest mozilla-central b2g build on travis

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https://hg.mozilla.org/integration/gaia-central/rev/676e8d3488cb
Author: James Lal <james@lightsofapollo.com>
Desc: Bug 919882 - Use latest mozilla-central b2g build on travis