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

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https://hg.mozilla.org/integration/gaia-central/rev/30de318e162e
Author: Arthur Chen <crh0716@gmail.com>
Desc: Merge pull request #12885 from crh0716/912020

Bug 912020 - Save to settings DB when leaving the panel r=evelyn

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https://hg.mozilla.org/integration/gaia-central/rev/d3dd79fc9fdb
Author: Arthur Chen <crh0716@gmail.com>
Desc: Bug 912020 - Save to settings DB when leaving the panel

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https://hg.mozilla.org/integration/gaia-central/rev/908ee9488b2a
Author: Dale Harvey <dale@arandomurl.com>
Desc: Bug 932795 - remove unused systemXHR permission. r=daleharvey