Fix unit_Test.ClientTest following 108015a

Closes #604

Author: dw

tests/unix_test.py

@@ -90,7 +90,7 @@ def _try_connect(self, path):
         while True:
             try:
                 return mitogen.unix.connect(path)
-            except socket.error:
+            except mitogen.unix.ConnectError:
                 if time.time() > timeout:
                     raise
                 time.sleep(0.1)