convert shebang lines: python -> python3
diff --git a/Doc/includes/email-unpack.py b/Doc/includes/email-unpack.py
index a8f712d..3653543 100644
--- a/Doc/includes/email-unpack.py
+++ b/Doc/includes/email-unpack.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 """Unpack a MIME message into a directory of files."""