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

========

https://hg.mozilla.org/integration/gaia-central/rev/6127157a7933
Author: Gareth Aye <gaye@mozilla.com>
Desc: Merge pull request #11564 from lightsofapollo/travis-mc

Bug 905875 - Switch unit tests to mozilla-central

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "29a1de78a742e6605d0bd20f8fc82b1371216fc3", 
+    "revision": "6127157a7933badbe075f894743a09c1152afe58", 
     "repo_path": "/integration/gaia-central"
 }