Fix concurrency issue with writes

pubsub.go

@@ -102,6 +102,9 @@ func (t *TwitchPubSub) Open() error {
 	if len(t.SubscribedTopics) > 0 {
 		return t.listen(t.SubscribedTopics)
 	} else {
+		t.wsMutex.Lock()
+		defer t.wsMutex.Unlock()
+		t.LastPing = time.Now()
 		return t.wsConn.WriteJSON(&twitchMessage{Type: Ping})
 	}