Bump express from 4.16.2 to 4.17.3 in /frontend

Bumps [express](https://github.com/expressjs/express) from 4.16.2 to 4.17.3.
- [Release notes](https://github.com/expressjs/express/releases)
- [Changelog](https://github.com/expressjs/express/blob/master/History.md)
- [Commits](expressjs/express@4.16.2...4.17.3)

---
updated-dependencies:
- dependency-name: express
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

frontend/package.json

@@ -29,7 +29,7 @@
     "antd": "^3.1.3",
     "axios": "^0.17.1",
     "body-parser": "^1.18.2",
-    "express": "^4.16.2",
+    "express": "^4.17.3",
     "immutable": "^3.8.2",
     "nuka-carousel": "^3.0.1",
     "prop-types": "^15.6.0",