convert shebang lines: python -> python3
diff --git a/Demo/zlib/zlibdemo.py b/Demo/zlib/zlibdemo.py
index 53463dd..52f71a0 100755
--- a/Demo/zlib/zlibdemo.py
+++ b/Demo/zlib/zlibdemo.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 # Takes an optional filename, defaulting to this file itself.
 # Reads the file and compresses the content using level 1 and level 9