example(plugin.json): align example app with latests version

examples/nginx-app/plugin.json

@@ -34,13 +34,10 @@
     "updated": "2015-02-10"
   },
 
-  "includes": {
-    "dashboards": [],
-    "plugins": [
+  "includes": [
       {"type": "panel", "name": "Nginx Panel"},
       {"type": "datasource", "name": "Nginx Datasource"}
-    ]
-  },
+  ],
 
   "dependencies": {
     "grafanaVersion": "3.x.x",