convert shebang lines: python -> python3
diff --git a/Demo/scripts/fact.py b/Demo/scripts/fact.py
index 71fcda2..2a3bef2 100755
--- a/Demo/scripts/fact.py
+++ b/Demo/scripts/fact.py
@@ -1,4 +1,4 @@
-#! /usr/bin/env python
+#! /usr/bin/env python3
 
 # Factorize numbers.
 # The algorithm is not efficient, but easy to understand.