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

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https://hg.mozilla.org/integration/gaia-central/rev/231a362c2610
Author: Casey Yee <cyee@mozilla.com>
Desc: Merge pull request #14140 from caseyyee/bug-941625

Bug 941625 - [Browser] Update background and sub header colour

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https://hg.mozilla.org/integration/gaia-central/rev/a042abb438d2
Author: Casey Yee <casey@caseyyee.com>
Desc: Bug 941625 - [Browser] Update background and sub header colour