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

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https://hg.mozilla.org/integration/gaia-central/rev/171943320172
Author: Jim Porter <squibblyflabbetydoo@gmail.com>
Desc: Merge pull request #13053 from jimporter/music-nowplaying-icon

Bug 930386 - Fix the "now playing" icon that gets sent to the system app; r=dkuo

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https://hg.mozilla.org/integration/gaia-central/rev/b8dc61d558b2
Author: Jim Porter <jporter@mozilla.com>
Desc: Fix the "now playing" icon that gets sent to the system app