Allow Python 3 detection when not using Django

Signed-off-by: Roberto Rosario <roberto.rosario@mayan-edms.com>

mayan/apps/storage/utils.py

@@ -7,7 +7,12 @@ import tempfile
 
 from pathlib2 import Path
 
-from django.utils.six import PY3
+try:
+    from django.utils.six import PY3
+except ImportError:
+    # This is being imported outside of Django
+    import sys
+    PY3 = sys.version_info[0] == 3
 
 from .settings import setting_temporary_directory