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

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https://hg.mozilla.org/integration/gaia-2_0/rev/386eaf5c636b
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #21560 from jimporter/ringtones-new-default-2.0

Bug 1031430 - (2.0-visual-refresh)[Notifications and Alarms] - Add New S...

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https://hg.mozilla.org/integration/gaia-2_0/rev/a8ec92415e1c
Author: Jim Porter <jporter@mozilla.com>
Desc: Bug 1031430 - (2.0-visual-refresh)[Notifications and Alarms] - Add New Signature Firefox OS tone
Bumping manifests a=b2g-bump