Bumping gaia.json for 2 gaia-central revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/7edf914c58bb
Author: Sam Joch <samuel@guiora.com>
Desc: Merge pull request #13988 from samjoch/bug-942098-HomescreenUpdateDockAndAppIconDropShadows

Bug 942098 - [Homescreen] Update Dock and App Icon drop shadows r=21

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https://hg.mozilla.org/integration/gaia-central/rev/b763ae0f0cfc
Author: Sam Joch <samuel@guiora.com>
Desc: Bug 942098 - [Homescreen] Update Dock and App Icon drop shadows