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

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https://hg.mozilla.org/integration/gaia-central/rev/46683f132535
Author: Jim Porter <jporter@mozilla.com>
Desc: Merge pull request #20940 from jimporter/ringtones-exclusive-mode

Bug 1020771 - When ringtone application is in background, music volume c...

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https://hg.mozilla.org/integration/gaia-central/rev/2a8d6cc9d44d
Author: Jim Porter <jporter@mozilla.com>
Desc: Bug 1020771 - When ringtone application is in background, music volume cant be changed
Bumping manifests a=b2g-bump