TypeError: buf expected bytes, got <class 'str'>

[FrankFortier]

Hello I got an error in server.py line 243

` def on_timeout(self):
"""
Callback received on session timeout.

    Default implementation writes "Timeout." bound by CRLF and closes.

    This can be disabled by calling :meth:`set_timeout` with
    :paramref:`~.set_timeout.duration` value of ``0`` or value of
    the same for keyword argument ``timeout``.
    """
    logger.debug("Timeout after {self.idle:1.2f}s".format(self=self))
    self.writer.write("\r\nTimeout.\r\n")  <=== Problematic line
    self.timeout_connection()

`