Use default python in executable.

pubs/pubs

@@ -1,5 +1,5 @@
-#!/usr/bin/env python2
+#!/usr/bin/env python
 # -*- coding:utf-8 -*-
 
 from pubs import pubs_cmd
-pubs_cmd.execute()
+pubs_cmd.execute()

pubs/pubs_cmd.py

@@ -1,5 +1,3 @@
-#!/usr/bin/env python2
-# -*- coding:utf-8 -*-
 import sys
 
 import argparse