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

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https://hg.mozilla.org/integration/gaia-central/rev/3acbd9057dc3
Author: Jim Porter <squibblyflabbetydoo@gmail.com>
Desc: Merge pull request #12314 from jimporter/music-notification-controls

Bug 902981 - [Music] [User Story] Provide access to music controls in the notifications tray

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https://hg.mozilla.org/integration/gaia-central/rev/20926d18037d
Author: Jim Porter <jporter@mozilla.com>
Desc: Bug 902981 - Add support for music playback controls from the notifications area; r=alive, r=djf, ui-r=robmac, ui-r=epang