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

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https://hg.mozilla.org/integration/gaia-central/rev/21fe48f22535
Author: Carsten Book -Tomcat- <cbook@mozilla.com>
Desc: Revert "Bug 946205 - Re-enable Travis tests after 891882 merged" for mochitest 5 timeouts

This reverts commit f7babc50d93bf153e527aeaf808b81f5017056c5.
Bumping manifests a=b2g-bump