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

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https://hg.mozilla.org/integration/gaia-central/rev/ac125ca91aec
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #23284 from KevinGrandon/bug_1058270_change_browser_role

Bug 1058270 - Hide the browser app by changing role to system

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https://hg.mozilla.org/integration/gaia-central/rev/fdf2ec3b1613
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 1058270 - Hide the browser app by changing role to system r=qdot
Bumping manifests a=b2g-bump