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

========

https://hg.mozilla.org/integration/gaia-central/rev/c541b74ca62d
Author: Carsten Book -Tomcat- <cbook@mozilla.com>
Desc: Revert "Bug 897352 - [gaia build system] Transition to a build_stage for assembling apps" build failure

This reverts commit c965501afb3849cb1b10b0738c86fe9e450e8b9a.

b2g/config/gaia.json

@@ -4,6 +4,6 @@
         "remote": "", 
         "branch": ""
     }, 
-    "revision": "657c17e410decab9a207ff5a00bdc9a738bd4980", 
+    "revision": "c541b74ca62d0d9e9e8d301ad67a214e6cff10e5", 
     "repo_path": "/integration/gaia-central"
 }