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

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https://hg.mozilla.org/integration/gaia-central/rev/dbc8bf7183da
Author: Rob Wood <rwood@mozilla.com>
Desc: Merge pull request #12404 from rwood-moz/update_endurance

Bug 920180 - Gaia-ui endurance test updates for master (sms and settings tests)

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https://hg.mozilla.org/integration/gaia-central/rev/d188ed480f16
Author: rwood-moz <rwood@mozilla.com>
Desc: Gaia-ui endurance test updates for master