convert shebang lines: python -> python3
diff --git a/Tools/scripts/untabify.py b/Tools/scripts/untabify.py
index 1a186a3..f21b7c8 100755
--- a/Tools/scripts/untabify.py
+++ b/Tools/scripts/untabify.py
@@ -1,4 +1,4 @@
-#! /usr/bin/env python
+#! /usr/bin/env python3
 
 "Replace tabs with spaces in argument files.  Print names of changed files."