Update dependency express to v4.17.1

Author: renovate-bot

plugin/multiplex/package.json

@@ -10,7 +10,7 @@
     "node": "~4.1.1"
   },
   "dependencies": {
-    "express": "~4.13.3",
+    "express": "4.17.1",
     "grunt-cli": "~0.1.13",
     "mustache": "~2.2.1",
     "socket.io": "~1.3.7"