py3 support errors

dtls/test/unit.py

@@ -281,7 +281,7 @@ class NetworkedTests(unittest.TestCase):
                     count += 1
                     s.do_handshake()
                     break
-                except ssl.SSLError, err:
+                except ssl.SSLError as err:
                     if err.args[0] == ssl.SSL_ERROR_WANT_READ:
                         while True:
                             to = s.get_timeout()