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

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https://hg.mozilla.org/integration/gaia-central/rev/b7125d6c8e4e
Author: George <georgeiscoming@gmail.com>
Desc: Merge pull request #11857 from cctuan/851189

Bug 851189 - Move feedback button up one level

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https://hg.mozilla.org/integration/gaia-central/rev/fa1eb84be0f4
Author: cctuan <georgeiscoming@gmail.com>
Desc: Bug 851189 - Move feedback button up one level

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https://hg.mozilla.org/integration/gaia-central/rev/9a2999a7a2e3
Author: Greg Weng <snowmantw@gmail.com>
Desc: Merge pull request #12784 from snowmantw/issue925635

Bug 925635 - [LockScreen] Fix the track to match the icons

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https://hg.mozilla.org/integration/gaia-central/rev/0a905b0061f2
Author: Greg Weng (snowmantw) <gweng@mozilla.com>
Desc: Bug 925635 - [LockScreen] Fix the track to match the icons
Bug 926880 - Enable IAC API for b2g-desktop. r=genelian