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

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https://hg.mozilla.org/integration/gaia-central/rev/912f59e40be2
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #26065 from KevinGrandon/bug_1081731_private_browsing

Bug 1081731 - Simple support for private browsing

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https://hg.mozilla.org/integration/gaia-central/rev/cc38a5f28458
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 1081731 - Add support for private browsing r=etienne
Bumping manifests a=b2g-bump