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

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https://hg.mozilla.org/integration/gaia-central/rev/8d9b7089df3a
Author: Dave Hunt <dave.hunt@gmail.com>
Desc: Bug 1003784 - Separate out FakeUpdateChecker.check_updates() and start_b2g(). r=zcampbell
Bumping manifests a=b2g-bump