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

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https://hg.mozilla.org/integration/gaia-central/rev/d5ebee6f3764
Author: Pavel Ivanov <pivanov@mozilla.com>
Desc: Merge pull request #13767 from pivanov/bug-939139

Bug 939139 - [Music] Update scrubber to be consistent with the video player

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https://hg.mozilla.org/integration/gaia-central/rev/88965740b73a
Author: Pavel Ivanov <pivanov@mozilla.com>
Desc: Bug 939139 - [Music] Update scrubber to be consistent with the video player