Fix usage of play.py for Arduino

[vincentbernat]

Otherwise, we get this error:

$ python3 play.py
Traceback (most recent call last):
  File "play.py", line 73, in <module>
    usage()
  File "play.py", line 31, in usage
    ''' % ((sys.argv[0],) * 5)
TypeError: not all arguments converted during string formatting