fix: cleanup websocket connections

Removed by accident here:
webtorrent@d079171044e0c1f84f9e
431b110358ad1ff2b20f#diff-78c12f5adc1848d13b1c6f07055d996eL602

Author: feross

server.js

@@ -610,6 +610,7 @@ Server.prototype._onWebSocketClose = function (socket) {
       var swarm = self.torrents[infoHash]
       if (swarm) {
         swarm.announce({
+          type: 'ws',
           event: 'stopped',
           numwant: 0,
           peer_id: socket.peerId