convert shebang lines: python -> python3
diff --git a/Demo/tkinter/guido/svkill.py b/Demo/tkinter/guido/svkill.py
index 0dd9f95..4ed88ad 100755
--- a/Demo/tkinter/guido/svkill.py
+++ b/Demo/tkinter/guido/svkill.py
@@ -1,4 +1,4 @@
-#! /usr/bin/env python
+#! /usr/bin/env python3
 
 # Tkinter interface to SYSV `ps' and `kill' commands.