Bump socket.io from 2.2.0 to 2.4.0 in /src/samples/conference (#459)

Bumps [socket.io](https://github.com/socketio/socket.io) from 2.2.0 to 2.4.0.
- [Release notes](https://github.com/socketio/socket.io/releases)
- [Changelog](https://github.com/socketio/socket.io/blob/2.4.0/CHANGELOG.md)
- [Commits](socketio/socket.io@2.2.0...2.4.0)

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

src/samples/conference/package-lock.json

@@ -17,7 +17,7 @@
     "errorhandler": "",
     "express": "",
     "morgan": "",
-    "socket.io": "^2.2.0",
+    "socket.io": "^2.4.0",
     "spdy": ""
   },
   "main": "samplertcservice.js",