umqtt.simple: Update for to_bytes() parameters refactor.

umqtt.simple/umqtt/simple.py

@@ -136,7 +136,7 @@ class MQTTClient:
         #print(hex(len(pkt)), hexlify(pkt, ":"))
         self.sock.write(pkt)
         self._send_str(topic)
-        self.sock.write(qos.to_bytes(1))
+        self.sock.write(qos.to_bytes(1, "little"))
         while 1:
             op = self.wait_msg()
             if op == 0x90: