Bump socket.io from 2.3.0 to 2.4.0 in /listener_clients/relay-listener

Bumps [socket.io](https://github.com/socketio/socket.io) from 2.3.0 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@2.3.0...2.4.0)

---
updated-dependencies:
- dependency-name: socket.io
  dependency-type: direct:production
...

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