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

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https://hg.mozilla.org/integration/gaia-2_1/rev/3efd56507b20
Author: Diego Marcos <diego.marcos@gmail.com>
Desc: Revert "Bug 1058288 - [PDF Viewer] Update pdf.js to version 1.0.696"
Bumping manifests a=b2g-bump