Bumping gaia.json for 4 gaia-central revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/df2257cbb908
Author: Dominic Kuo <dkuo@mozilla.com>
Desc: Merge pull request #15141 from dominickuo/bug-949845

Bug 949845 - [music] hide the cover controls for music open activity, r=jimporter

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https://hg.mozilla.org/integration/gaia-central/rev/4a16437a10bf
Author: Dominic Kuo <dkuo@mozilla.com>
Desc: Bug 949845 - [music] hide the cover controls for music open activity

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https://hg.mozilla.org/integration/gaia-central/rev/9eb641e673cb
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #14122 from svic/handover

Bug 933093 - Implementation of HandoverManager for file transfer

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https://hg.mozilla.org/integration/gaia-central/rev/e9202e371702
Author: Arno Puder <arno@puder.org>
Desc: Bug 933093 - Implementation of HandoverManager for file transfer