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

========

https://hg.mozilla.org/integration/gaia-central/rev/cef0c9746df8
Author: Zac <zcampbell@mozilla.com>
Desc: Bug 967908 Fix timing in test_sms_contact_validation r=me a=testonly

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "8720f41b0ad52dbc3c9f59d44a9a8f257cb01136", 
+    "revision": "cef0c9746df83433d45220f9556ca32377ad9943", 
     "repo_path": "/integration/gaia-central"
 }