Do not consider broken layergroup configs as good on second look

The fix is really in Windshaft, this commit simply requires a
newer version of it.

npm-shrinkwrap.json

@@ -9,7 +9,7 @@
       "version": "1.3.3"
     },
     "windshaft": {
-      "version": "0.12.8",
+      "version": "0.12.9",
       "dependencies": {
         "grainstore": {
           "version": "0.13.5",

package.json

@@ -20,7 +20,7 @@
     "dependencies": {
         "node-varnish": "0.1.1",
         "underscore"  : "~1.3.3",
-        "windshaft"  : "~0.12.8",
+        "windshaft"  : "~0.12.9",
         "step": "0.0.x",
         "generic-pool": "~2.0.3",
         "redis": "~0.8.3",