Bump socket.io from 2.2.0 to 2.4.0

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] <support@github.com>

package.json

@@ -174,7 +174,7 @@
     "serialize-javascript": "^1.6.1",
     "serve-favicon": "^2.5.0",
     "shelljs": "^0.7.5",
-    "socket.io": "^2.2.0",
+    "socket.io": "^2.4.0",
     "socket.io-client": "^2.2.0",
     "stats-webpack-plugin": "^0.2.1",
     "superagent": "^3.8.3",