Bumping gaia.json for 6 gaia-central revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/f256e81f9717
Author: Fabrice Desré <fabrice@desre.org>
Desc: Merge pull request #14285 from cvan/updated-mkt

Bug 942355 - Update Marketplace packaged app for dual SIM detection

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https://hg.mozilla.org/integration/gaia-central/rev/98279412a1f1
Author: Chris Van <cvan@mozilla.com>
Desc: Bug 942355 - Update Marketplace packaged app for dual SIM detection r=fabrice

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https://hg.mozilla.org/integration/gaia-central/rev/1736c7d1848b
Author: Pavel Ivanov <pivanov@mozilla.com>
Desc: Merge pull request #14079 from pivanov/bug-939209

Bug 939209 - [Action Icons - Email] Remove shadows from action icons

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https://hg.mozilla.org/integration/gaia-central/rev/af99e39bd529
Author: Pavel Ivanov <pivanov@mozilla.com>
Desc: Bug 939209 - [Action Icons - Email] Remove shadows from action icons

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https://hg.mozilla.org/integration/gaia-central/rev/ddb2560e03ee
Author: Pavel Ivanov <pivanov@mozilla.com>
Desc: Merge pull request #14513 from pivanov/bug-930600

Bug 930600 - Add new Illustrative Wallpapers for v.1.3

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https://hg.mozilla.org/integration/gaia-central/rev/5dfcaaefd217
Author: Pavel Ivanov <pivanov@mozilla.com>
Desc: Bug 930600 - Add new Illustrative Wallpapers for v.1.3