Bumping gaia.json for 1 gaia-1_2 revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-1_2/rev/8dd5aedd82c4
Author: Dale Harvey <dale@arandomurl.com>
Desc: Bug 932795 - remove unused systemXHR permission. r=daleharvey

(cherry picked from commit 8179e273ebf9c1384f57a0813394bef294b51aad)