socket.io dependency

package.json

@@ -19,6 +19,7 @@
     "morgan": "~1.9.0",
     "pug": "2.0.0-beta11",
     "serve-favicon": "~2.4.5",
+    "socket.io": "^2.1.1",
     "supervisor": "^0.12.0"
   }
 }