版本：2.3.0
- https://cdn.bootcdn.net/ajax/libs/socket.io/2.3.0/socket.io.dev.
- https://cdn.bootcdn.net/ajax/libs/socket.io/2.3.0/socket.io.
- https://cdn.bootcdn.net/ajax/libs/socket.io/2.3.0/socket.io.slim.dev.
- https://cdn.bootcdn.net/ajax/libs/socket.io/2.3.0/socket.io.slim.