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

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https://hg.mozilla.org/integration/gaia-central/rev/f8248c26e183
Author: Eitan Isaacson <eitan@monotonous.org>
Desc: Merge pull request #13762 from eeejay/bug-938931

Bug 938931 - [FTU] Fix checkbox regressions from bug #914892. r=fcampo

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https://hg.mozilla.org/integration/gaia-central/rev/72a863401491
Author: Eitan Isaacson <eitan@monotonous.org>
Desc: Bug 938931 - [FTU] Fix checkbox regressions from bug #914892

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https://hg.mozilla.org/integration/gaia-central/rev/b29331057651
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #13782 from pivanov/bug-939148

Bug 939148 - [Action Icons - Calendar] Remove shadows from action icons r=kgrandon

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https://hg.mozilla.org/integration/gaia-central/rev/bbd669bcf8f3
Author: Pavel Ivanov <pivanov@mozilla.com>
Desc: Bug 939148 - [Action Icons - Calendar] Remove shadows from action icons