convert shebang lines: python -> python3
diff --git a/Demo/tkinter/guido/rmt.py b/Demo/tkinter/guido/rmt.py
index 7b3f700..a3f430e 100755
--- a/Demo/tkinter/guido/rmt.py
+++ b/Demo/tkinter/guido/rmt.py
@@ -1,4 +1,4 @@
-#! /usr/bin/env python
+#! /usr/bin/env python3
 
 # A Python program implementing rmt, an application for remotely
 # controlling other Tk applications.