asn1tostruct.py: specify python version in shebang

The script is expected to be run using python 2.x, but nowadays some
distros are already using python 3 as default, which will fail to run
this script.

This change fixes compilation in my Archlinux box.

Change-Id: I6eb95351538a64f2b23d638824972818591b1b66

asn1/utils/asn1tostruct.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python2
 
 import re, os, sys, string
 import datetime