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

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https://hg.mozilla.org/integration/gaia-2_1/rev/819e11e645ad
Author: Fabrice Desré <fabrice@desre.org>
Desc: Bug 1074107 - Add wallpaper test themes to dev-apps. r=fabrice
Bumping manifests a=b2g-bump