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

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https://hg.mozilla.org/integration/gaia-central/rev/464bfafbe960
Author: Pavel Ivanov <pivanov@mozilla.com>
Desc: Merge pull request #12907 from pivanov/bug-917895

Bug 917895 - [Email] Update Unread Count Banner

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https://hg.mozilla.org/integration/gaia-central/rev/6057eebf02d3
Author: Pavel Ivanov <pivanov@mozilla.com>
Desc: Bug 917895 - [Email] Update Unread Count Banner
Bumping gaia.json for 2 gaia-central revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/0c2ae3f386f2
Author: Pavel Ivanov <pivanov@mozilla.com>
Desc: Merge pull request #12901 from pivanov/bug-917808

Bug 917808 - [Music] Generic album art overlaps hairline

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https://hg.mozilla.org/integration/gaia-central/rev/0018198d4ce8
Author: Pavel Ivanov <pivanov@mozilla.com>
Desc: Bug 917808 - [Music] Generic album art overlaps hairline