Add classifier for Python 3.6.

Author: GrahamDumpleton

setup.py

@@ -570,6 +570,7 @@ def _version():
         'Programming Language :: Python :: 3.3',
         'Programming Language :: Python :: 3.4',
         'Programming Language :: Python :: 3.5',
+        'Programming Language :: Python :: 3.6',
         'Topic :: Internet :: WWW/HTTP :: WSGI',
         'Topic :: Internet :: WWW/HTTP :: WSGI :: Server'
     ],