convert shebang lines: python -> python3
diff --git a/Doc/includes/email-dir.py b/Doc/includes/email-dir.py
index e67de61..b1b45b8 100644
--- a/Doc/includes/email-dir.py
+++ b/Doc/includes/email-dir.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 """Send the contents of a directory as a MIME message."""