Use "#!/usr/bin/env python2.7" only in utilities
diff --git a/tools/run_tests/antagonist.py b/tools/run_tests/antagonist.py
index 111839c..857addf 100755
--- a/tools/run_tests/antagonist.py
+++ b/tools/run_tests/antagonist.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python2.7
 # Copyright 2015, Google Inc.
 # All rights reserved.
 #