add ipaddress to setup.py

setup.py

@@ -1,8 +1,15 @@
 #!/usr/bin/env python
 # -*- encoding: utf-8 -*-
 
+import sys
+
 from setuptools import setup, find_packages
 
+requires = ['Jinja2>=2.7', 'werkzeug>=0.9', 'itsdangerous', 'misaka', 'html5lib']
+
+if sys.version_info < (3, 0):
+    requires += ['ipaddress']
+
 setup(
     name='isso',
     version='0.1',
@@ -23,7 +30,7 @@ setup(
         "Programming Language :: Python :: 2.6",
         "Programming Language :: Python :: 2.7"
     ],
-    install_requires=['Jinja2>=2.7', 'werkzeug>=0.9', 'itsdangerous', 'misaka', 'html5lib'],
+    install_requires=requires,
     entry_points={
         'console_scripts':
             ['isso = isso:main'],