convert shebang lines: python -> python3
diff --git a/Demo/turtle/tdemo_clock.py b/Demo/turtle/tdemo_clock.py
index e186c38..a0d157b 100644
--- a/Demo/turtle/tdemo_clock.py
+++ b/Demo/turtle/tdemo_clock.py
@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python3
 # -*- coding: cp1252 -*-
 """       turtle-example-suite: