[fix] modbus serial_conn.open

pyheatpump/modbus.py

             timeout=20)
 
     if serial_conn.open is False:
-        logger.debug('Opening serial port *%s*', config.get('heatpump', 'serial_port')
+        logger.debug('Opening serial port *%s*', 
+            config.get('heatpump', 'serial_port'))
         serial_conn.open()
 
     return serial_conn