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/31f95a17ff5e
Author: Sebastiaan de Haan <me@sebastiaandehaan.nl>
Desc: Bug 818287 - Support screenshots without a data URL prefix. r=dhunt