convert shebang lines: python -> python3
diff --git a/Lib/mailbox.py b/Lib/mailbox.py
index 3f299a8..c2c9b5c 100755
--- a/Lib/mailbox.py
+++ b/Lib/mailbox.py
@@ -1,4 +1,4 @@
-#! /usr/bin/env python
+#! /usr/bin/env python3
 
 """Read/write support for Maildir, mbox, MH, Babyl, and MMDF mailboxes."""