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

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https://hg.mozilla.org/integration/gaia-central/rev/cb0835086e34
Author: Sam Joch <samuel@guiora.com>
Desc: Merge pull request #11668 from pivanov/bug-907818

Bug 907818 - [First Time Experience] [HD] Grey background blurry r=samjoch

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https://hg.mozilla.org/integration/gaia-central/rev/8ce7bbdca04c
Author: Pavel Ivanov <pivanov@mozilla.com>
Desc: Bug 907818 - [First Time Experience] [HD] Grey background blurry