cryptsuite: switch #! line to Python 3.

Since I apparently can't reliably keep this script working on both
flavours of Python, I think these days I'd rather it broke on 2 than
on 3 due to my inattention. So let's default to 3.

test/cryptsuite.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 import unittest
 import struct