[chore] Update the license of the chat example (#3410)
[chore] Update the license of the chat example (#3410)

There was no obvious reason to use BSD instead of MIT for that very basic chat app.

Closes #3411
Automattic/socket.io,Automattic/socket.io,socketio/socket.io,mosoft521/socket.io,socketio/socket.io,mosoft521/socket.io,SimenB/socket.io