Fix install error on python 2.7

alejandroautalan · alejandroautalan · commit b8028d47d52c · 2021-11-17T22:03:43.000-03:00
diff --git a/setup.py b/setup.py
@@ -8,6 +8,7 @@
     python3-tk
 """
 import os
+from io import open
 
 import pygubu
 
