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

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https://hg.mozilla.org/integration/gaia-2_1/rev/cb2dceaf3336
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Revert "Bug 1069157 - [PDF Viewer] update pdf.js in Gaia"

This reverts commit 3b815d4c88bf137f1a9a52b8a5373b94a012a7f3.
Bumping manifests a=b2g-bump