Add environment markers to django test dependency (#460)

Author: Jon Wayne Parrott

tox.ini

@@ -13,7 +13,8 @@ deps =
        mox
        pyopenssl
        pycrypto==2.6
-       django
+       django<2.0.0; python_version < '3.0.0'
+       django>=2.0.0; python_version > '3.0.0'
        webtest
        nose
        coverage>=3.6,<3.99