chore(package): update express to version 4.15.0

https://greenkeeper.io/

Author: greenkeeperio-bot

package.json

@@ -31,7 +31,7 @@
     "compression": "1.2.2",
     "cookie-parser": "1.3.3",
     "debuglog": "1.0.1",
-    "express": "4.13.3",
+    "express": "4.15.0",
     "fs-extra": "0.18.3",
     "lodash": "3.10.1",
     "method-override": "2.3.7",