use /usr/bin/env to reach python

followup to 419c1246c128ad4b37a0eb0050c77cd401257b98

tools/starpu_trace_state_stats.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 # -*- coding: utf-8 -*-
 # StarPU --- Runtime system for heterogeneous multicore architectures.
 #