Update express requirement from ~4.15.5 to ~4.17.1

Updates the requirements on [express](https://github.com/expressjs/express) to permit the latest version.
- [Release notes](https://github.com/expressjs/express/releases)
- [Changelog](https://github.com/expressjs/express/blob/master/History.md)
- [Commits](expressjs/express@4.15.5...4.17.1)

package.json

@@ -23,7 +23,7 @@
     "body-parser": "~1.18.2",
     "cookie-parser": "~1.4.3",
     "debug": "~2.6.9",
-    "express": "~4.15.5",
+    "express": "~4.17.1",
     "jquery": "^3.2.1",
     "level": "^2.1.1",
     "morgan": "~1.9.0",