tools: use '/usr/bin/env python' instead of '/usr/bin/python'

* This is how it is done in other scripts in the AOSP tree, as
  '/usr/bin/python' may be python3 on some distros, which isn't
  supported yet.

Change-Id: I0d9857fc6a122f505953fddcd6244dad75b1838a
diff --git a/tools/cpplint.py b/tools/cpplint.py
index 30b5216..c2f6514 100755
--- a/tools/cpplint.py
+++ b/tools/cpplint.py
@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 #
 # Copyright (c) 2009 Google Inc. All rights reserved.
 #