Fix python command for clang checks (2 -> 3).

bin/clang-tidy-diff.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 #===- clang-tidy-diff.py - ClangTidy Diff Checker ------------*- python -*--===#
 #

bin/run-clang-format.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 """A wrapper script around clang-format, suitable for linting multiple files
 and to use for continuous integration.