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

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https://hg.mozilla.org/integration/gaia-central/rev/3890e38ebe08
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #22931 from KevinGrandon/bug_1054320_ftu_colors

Bug 1054320 - [FTU] Update dark themed pages to match new system colors

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https://hg.mozilla.org/integration/gaia-central/rev/52856a68458a
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 1054320 - [FTU] Update dark themed pages to match new system colors r=fcampo
Bumping manifests a=b2g-bump