convert shebang lines: python -> python3
diff --git a/Demo/scripts/beer.py b/Demo/scripts/beer.py
index 8135509..56eec7b 100755
--- a/Demo/scripts/beer.py
+++ b/Demo/scripts/beer.py
@@ -1,4 +1,4 @@
-#! /usr/bin/env python
+#! /usr/bin/env python3
 
 # By GvR, demystified after a version by Fredrik Lundh.