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

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https://hg.mozilla.org/integration/gaia-central/rev/e885f915f898
Author: autolander <bug.autolander@gmail.com>
Desc: Bug 1039639 - merge pull request #25904 from jimporter:music-flac to mozilla-b2g:master

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https://hg.mozilla.org/integration/gaia-central/rev/6cabaa0ac204
Author: Jim <jporter@mozilla.com>
Desc: Bug 1039639 - [music] Support parsing FLAC metadata
Bumping manifests a=b2g-bump