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

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https://hg.mozilla.org/integration/gaia-central/rev/b8c45712ab35
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Merge pull request #16680 from timdream/lockscreen-background2

Bug 971654 - Correct lockscreen background sizing, r=snowmantw

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https://hg.mozilla.org/integration/gaia-central/rev/dbbb28d7c8f1
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Bug 971654 - Correct lockscreen background sizing

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https://hg.mozilla.org/integration/gaia-central/rev/c1bdf58fbd08
Author: Dominic Kuo <dkuo@mozilla.com>
Desc: Merge pull request #16560 from dominickuo/bug-961984

Bug 961984 - [Music] check the play status in playpause() and call playpause() in play(), r=jimporter

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https://hg.mozilla.org/integration/gaia-central/rev/fa0de74ee2da
Author: Dominic Kuo <dkuo@mozilla.com>
Desc: Bug 961984 - [Music] check the play status in playpause() and call playpause() in play()
Bumping manifests a=b2g-bump