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

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https://hg.mozilla.org/integration/gaia-2_1/rev/e90381520d5b
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Revert "Bug 1055299: Ignore continuous app launch request in homescreen side and send homescreen to background while rocketbar is open in system side"

This reverts commit b866e8a70fda3ab5987e6f3b4c6e91788b91a08e.
Bumping manifests a=b2g-bump