convert shebang lines: python -> python3
diff --git a/Demo/tkinter/guido/solitaire.py b/Demo/tkinter/guido/solitaire.py
index b2a2a66..375bd03 100755
--- a/Demo/tkinter/guido/solitaire.py
+++ b/Demo/tkinter/guido/solitaire.py
@@ -1,4 +1,4 @@
-#! /usr/bin/env python
+#! /usr/bin/env python3
 
 """Solitaire game, much like the one that comes with MS Windows.