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

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https://hg.mozilla.org/integration/gaia-central/rev/4bb99e10153c
Author: Francisco Jordano <arcturus@ardeenelinfierno.com>
Desc: Merge pull request #14372 from Joshua-S/bug-945545

[Bug 945545] - [FTE] Update background color to #F4F4F4

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https://hg.mozilla.org/integration/gaia-central/rev/19d131b94277
Author: Joshua Smith <joshua-smith@verizon.net>
Desc: [Bug 945545] - [FTE] Update background color to #F4F4F4