Bump socket.io from 2.1.1 to 2.4.0

Bumps [socket.io](https://github.com/socketio/socket.io) from 2.1.1 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@2.1.1...2.4.0)

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

Author: dependabot[bot]