Use python3 instead of python (which uses python 2)

--- a/vendor/gprof2dot/gprof2dot.py
+++ b/vendor/gprof2dot/gprof2dot.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # Copyright 2008-2009 Jose Fonseca
 #
--- a/vendor/gprof2dot/hotshotmain.py
+++ b/vendor/gprof2dot/hotshotmain.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # Copyright 2007 Jose Fonseca
 #