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

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https://hg.mozilla.org/integration/gaia-central/rev/2504fef13b88
Author: David Flanagan <dflanagan@mozilla.com>
Desc: Merge pull request #10616 from es92/music2-squashed

Prototype Music2 App

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https://hg.mozilla.org/integration/gaia-central/rev/6d53409222fe
Author: Evan Shapiro <evan.a.shapiro@gmail.com>
Desc: music2 app prototype