fix(deps): update dependency express to v4.20.0 [security]

Author: renovate[bot]

template/slides/reveal/plugin/multiplex/package.json

@@ -10,7 +10,7 @@
     "node": "~4.1.1"
   },
   "dependencies": {
-    "express": "4.13.4",
+    "express": "4.20.0",
     "grunt-cli": "0.1.13",
     "mustache": "2.2.1",
     "socket.io": "1.3.7"