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

========

https://hg.mozilla.org/integration/gaia-central/rev/a28d5864a243
Author: Alexandre Lissy <lissyx+github@lissyx.dyndns.org>
Desc: Revert "Merge pull request #12911 from lissyx/bug906296"

This reverts commit b9520ca7b28e469c91efd851e7af9ad7b38ee3ed, reversing
changes made to bc2fb252092af20050551ecbd7c5a3edab77b58e.

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "dbe7543ce99b1a503bea1129bcfc33bc35a981fb", 
+    "revision": "a28d5864a2430f817c89d3c5c2f5dd288812853f", 
     "repo_path": "/integration/gaia-central"
 }