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

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https://hg.mozilla.org/integration/gaia-2_1/rev/8c47620e78f0
Author: Dominic Kuo <dkuo@mozilla.com>
Desc: Revert "Bug 1082938 - [Music] set play status to playing when play event fires"

This reverts commit b83c9c8d9b03044f99515391f4a42d13ecc87fda.
Bumping manifests a=b2g-bump