testplan2html: make executable

Change-Id: Ie69193df5acf40a1b629e71e8baa07e6b99f8694
Signed-off-by: Nicolas Dechesne <nicolas.dechesne@linaro.org>
diff --git a/plans/testplan2html.py b/plans/testplan2html.py
old mode 100644
new mode 100755
index 69b9cb3..746df4d
--- a/plans/testplan2html.py
+++ b/plans/testplan2html.py
@@ -1,3 +1,5 @@
+#!/usr/bin/env python3
+
 import collections
 import datetime
 import logging