convert shebang lines: python -> python3
diff --git a/Demo/tkinter/guido/kill.py b/Demo/tkinter/guido/kill.py
index 36caba6..dd01a2d 100755
--- a/Demo/tkinter/guido/kill.py
+++ b/Demo/tkinter/guido/kill.py
@@ -1,4 +1,4 @@
-#! /usr/bin/env python
+#! /usr/bin/env python3
 # Tkinter interface to Linux `kill' command.
 
 from tkinter import *