examples/listen_uroboros.py is broken

[zachriggle]

~/pwntools ❯❯❯ gco upstream/master                                                                                 ⏎
HEAD is now at 1183fe4... Fixed a bug where readthedocs did not have rop documentation
~/pwntools ❯❯❯ python examples/listen_uroboros.py
[+] Trying to bind to 0.0.0.0 on port 1337: OK
[|] Waiting for connections on 0.0.0.0:1337
[/.......] Trying to bind to 0.0.0.0 on port 1337: Trying 0.0.0.0
Traceback (most recent call last):
  File "examples/listen_uroboros.py", line 8, in <module>
    cs = [listen(1337) for _ in range(3)]
  File "/home/user/pwntools/pwnlib/tubes/listen.py", line 58, in __init__
    listen_sock.bind(self.sockaddr)
  File "/home/user/.pyenv/versions/2.7.8/lib/python2.7/socket.py", line 224, in meth
    return getattr(self._sock,name)(*args)
socket.error: [Errno 98] Address already in use

[TethysSvensson]

Fixed in cb9d535.