Bump express from 4.17.1 to 4.17.3 in /posts-service

Bumps [express](https://github.com/expressjs/express) from 4.17.1 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@4.17.1...4.17.3)

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

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

Author: dependabot[bot]

posts-service/package-lock.json

@@ -15,7 +15,7 @@
     "body-parser": "^1.19.0",
     "cors": "^2.8.5",
     "crypto": "^1.0.1",
-    "express": "^4.17.1",
+    "express": "^4.17.3",
     "nodemon": "^2.0.12"
   }
 }