build: make sure we are calling python3 in all scripts

Jira: ZEP-1759
Change-Id: I0fc7329f806ca0049c555d3402dd145e92e54028
Signed-off-by: Anas Nashif <anas.nashif@intel.com>
diff --git a/scripts/devicetree.py b/scripts/devicetree.py
index bc65acc..4ff7f97 100755
--- a/scripts/devicetree.py
+++ b/scripts/devicetree.py
@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python3
 #
 # Copyright (c) 2017 Intel Corporation
 #