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

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https://hg.mozilla.org/integration/gaia-central/rev/ac08ef4ff88a
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #12584 from bobsilverberg/bug922687

Bug 922687 - Enable test_everythingme_launch_packaged_app against Travis-TBPL desktop builds, r=zac

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https://hg.mozilla.org/integration/gaia-central/rev/df84cce31050
Author: Bob Silverberg <bob.silverberg@gmail.com>
Desc: Bug 922687 - Enable test_everythingme_launch_packaged_app against Travis-TBPL desktop builds, r=zac

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https://hg.mozilla.org/integration/gaia-central/rev/7393287f6d4a
Author: gasolin <gasolin@gmail.com>
Desc: Merge pull request #12607 from gasolin/issue-921404

Bug 921404 - [Flatfish][Lockscreen] screen clock is too small on tablet, r=timdream

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https://hg.mozilla.org/integration/gaia-central/rev/df1c1d25e87c
Author: gasolin <gasolin@gmail.com>
Desc: Bug 921404 - [Flatfish][Lockscreen] screen clock is too small on tablet