django-appconf version not specified, incompatible version installed when using python 2

[unformatt]

https://github.com/georgemarshall/django-cryptography/blob/a5e5c5da834cd1194975187ec0cbf50be8934e1d/requirements.txt#L3

django-cryptography==0.3

During pip install with python 2.7:

   File "/usr/local/lib/python2.7/site-packages/appconf/base.py", line 107
     class AppConf(metaclass=AppConfMetaClass):
                            ^
 SyntaxError: invalid syntax