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

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https://hg.mozilla.org/integration/gaia-central/rev/27b36387e1e1
Author: Carsten Book -Tomcat- <cbook@mozilla.com>
Desc: Revert "Bug 897352 - [gaia build system] Transition to a build_stage for assembling apps" for bustage

This reverts commit 498250413b65c91762fd6f62e21b9f81c5ee77c9.
Bumping manifests a=b2g-bump