normalize shebang lines to #!/usr/bin/env python
diff --git a/Demo/turtle/tdemo_tree.py b/Demo/turtle/tdemo_tree.py
index 3c7178c..6fc8735 100644
--- a/Demo/turtle/tdemo_tree.py
+++ b/Demo/turtle/tdemo_tree.py
@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 """      turtle-example-suite:
 
              tdemo_tree.py