Bumping gaia.json for 3 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/8b562113c66b
Author: Luke Chang <lchang@mozilla.com>
Desc: Merge pull request #21853 from begeeben/1039931_replace__proto__

Bug 1039931 - [gaia][system] Replace __proto__ with Object.create, r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/f15b2ba97acb
Author: Yi-Fan Liao <begeeben@gmail.com>
Desc: Bug 1039931 - [gaia][system] Replace __proto__ with Object.create

* Remove usages of __proto__ in the system app.

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https://hg.mozilla.org/integration/gaia-central/rev/9f9a68779fc2
Author: Dale Harvey <dale@arandomurl.com>
Desc: Bug 1038326 - Fix layout issues with searchWindow and children. r=alive
Bumping manifests a=b2g-bump