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

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https://hg.mozilla.org/integration/gaia-central/rev/48891c349bfb
Author: Dominic Kuo <dkuo@mozilla.com>
Desc: Merge pull request #13629 from dominickuo/bug-936385

Bug 936385 - [music2] Re-layout the whole UI, r=@dominickuo

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https://hg.mozilla.org/integration/gaia-central/rev/327c22906035
Author: Evan Shapiro <evan.a.shapiro@gmail.com>
Desc: Bug 936385: Re-layout Music2 UI