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/a2308d075e50
Author: Gabriele Svelto <gsvelto@mozilla.com>
Desc: Bug 944242 - Properly handle do-not-track options when upgrading from 1.1 r=kaze