convert shebang lines: python -> python3
diff --git a/Doc/tools/rstlint.py b/Doc/tools/rstlint.py
index eaaf257..8e6b374 100755
--- a/Doc/tools/rstlint.py
+++ b/Doc/tools/rstlint.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 
 # Check for stylistic and formal issues in .rst and .py