Invocation fix.

client/connection.js

@@ -55,7 +55,7 @@ Connection.prototype.onOpen = function() {
     this.retryCounter = 0;
 
     clearTimeout(this.heartbeatTimer);
-    this.heartbeatTimer = setTimeout(this.ws.send.bind(null, { type: 'heartbeat' }), 30000);
+    this.heartbeatTimer = setTimeout(() => { this.ws.send({ type: 'heartbeat' }); }, 30000);
 
     const evt = new Event('L-conn-open');
     document.dispatchEvent(evt);