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

========

https://hg.mozilla.org/integration/gaia-central/rev/9d76b9a19325
Author: Fabrice Desré <fabrice@desre.org>
Desc: Bug 919579 - Silent the SINGLE_VARIANT_CONF_FILE loading error r=vingtetun

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "609201aba1a427e086906301c1fc86e586499529", 
+    "revision": "9d76b9a193252f1e383138588d3c4d1a9650f15a", 
     "repo_path": "/integration/gaia-central"
 }