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

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https://hg.mozilla.org/integration/gaia-central/rev/2815b6670938
Author: Zac Campbell <zcampbell@mozilla.com>
Desc: Bug 917525 - Unxfail test_clock_turn_on_off_alarm.py r=bebe