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

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https://hg.mozilla.org/integration/gaia-central/rev/e3564b8656fc
Author: James Lal <james@lightsofapollo.com>
Desc: Merge pull request #13073 from lightsofapollo/shepherd-beta

Bug 930578 - add shepherd docs +shepherd

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https://hg.mozilla.org/integration/gaia-central/rev/2178197ec5de
Author: James Lal <james@lightsofapollo.com>
Desc: Bug 930578 - add shepherd docs +shepherd