Django 2 compatibility

[shacker]

Enabling the middleware as documented in Django 2.x produces the following error on startup:

TypeError: __init__() takes 1 positional argument but 2 were given

Full traceback includes nothing helpful:

Unhandled exception in thread started by <function check_errors.<locals>.wrapper at 0x110da8268>
Traceback (most recent call last):
  File "/Users/shacker/.local/share/virtualenvs/iris-E1jYNxJE/lib/python3.6/site-packages/django/utils/autoreload.py", line 225, in wrapper
    fn(*args, **kwargs)
  File "/Users/shacker/.local/share/virtualenvs/iris-E1jYNxJE/lib/python3.6/site-packages/django/core/management/commands/runserver.py", line 140, in inner_run
    handler = self.get_handler(*args, **options)
  File "/Users/shacker/.local/share/virtualenvs/iris-E1jYNxJE/lib/python3.6/site-packages/django/contrib/staticfiles/management/commands/runserver.py", line 27, in get_handler
    handler = super().get_handler(*args, **options)
  File "/Users/shacker/.local/share/virtualenvs/iris-E1jYNxJE/lib/python3.6/site-packages/django/core/management/commands/runserver.py", line 65, in get_handler
    return get_internal_wsgi_application()
  File "/Users/shacker/.local/share/virtualenvs/iris-E1jYNxJE/lib/python3.6/site-packages/django/core/servers/basehttp.py", line 44, in get_internal_wsgi_application
    return import_string(app_path)
  File "/Users/shacker/.local/share/virtualenvs/iris-E1jYNxJE/lib/python3.6/site-packages/django/utils/module_loading.py", line 17, in import_string
    module = import_module(module_path)
  File "/Users/shacker/.local/share/virtualenvs/iris-E1jYNxJE/lib/python3.6/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 994, in _gcd_import
  File "<frozen importlib._bootstrap>", line 971, in _find_and_load
  File "<frozen importlib._bootstrap>", line 955, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 665, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 678, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/Users/shacker/dev/iris/iris/config/wsgi.py", line 9, in <module>
    application = get_wsgi_application()
  File "/Users/shacker/.local/share/virtualenvs/iris-E1jYNxJE/lib/python3.6/site-packages/django/core/wsgi.py", line 13, in get_wsgi_application
    return WSGIHandler()
  File "/Users/shacker/.local/share/virtualenvs/iris-E1jYNxJE/lib/python3.6/site-packages/django/core/handlers/wsgi.py", line 140, in __init__
    self.load_middleware()
  File "/Users/shacker/.local/share/virtualenvs/iris-E1jYNxJE/lib/python3.6/site-packages/django/core/handlers/base.py", line 39, in load_middleware
    mw_instance = middleware(handler)
TypeError: __init__() takes 1 positional argument but 2 were given