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

========

https://hg.mozilla.org/integration/gaia-central/rev/f400eac8b283
Author: b2gautomation <jonallengriffin@gmail.com>
Desc: Bug 907941 - gaia-ui-tests-pushbot (see bug)

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "99bfb07777033a2b96f4e7b047dc6cde24b2f02d", 
+    "revision": "f400eac8b28353050ea9ff87dcb7e780e3537a89", 
     "repo_path": "/integration/gaia-central"
 }