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

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https://hg.mozilla.org/integration/gaia-2_0/rev/391b4e7e23bf
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Revert "Bug 1039955 - Fix direct circular activity by closing front windows"

This reverts commit b75c7fdae7d9328297fa6363d59f96170a609245.
Bumping manifests a=b2g-bump