Django 1.10 middleware#6

Great work, Mr Weber. I found an issue though, the code isn't currently compatible with the recent change to middleware in Django 1.10. I'm sorry, I don't have time today to submit a pull request but to fix it, 1) add `from django.utils.deprecation import MiddlewareMixin` to the top of the middleware.py file and 2) change `class JWTAuthMiddleware(object):` to `class JWTAuthMiddleware(MiddlewareMixin):`. That's it. It should be backward compatible but I haven't had chance to test it.