Update dependency express to v4

Author: mend-for-github-com[bot]

samples/dynamic-html/package.json

@@ -6,7 +6,7 @@
     "node": ">= 0.8.x"
   },
   "dependencies": {
-    "express": "3.x"
+    "express": "4.x"
   },
   "license": "Unlicense"
 }