Fix CORS misconfiguration in socket.io (#1487)

Signed-off-by: Marinov Avgustin <[email protected]>

docs/static/slides/plugin/multiplex/package.json

@@ -13,7 +13,7 @@
     "express": "~4.13.3",
     "grunt-cli": "~0.1.13",
     "mustache": "~2.2.1",
-    "socket.io": "~1.3.7"
+    "socket.io": "~2.4.0"
   },
   "license": "MIT"
 }