convert shebang lines: python -> python3
diff --git a/Demo/scripts/update.py b/Demo/scripts/update.py
index d49e4b3..49c09d8 100755
--- a/Demo/scripts/update.py
+++ b/Demo/scripts/update.py
@@ -1,4 +1,4 @@
-#! /usr/bin/env python
+#! /usr/bin/env python3
 
 # Update a bunch of files according to a script.
 # The input file contains lines of the form <filename>:<lineno>:<text>,