update to middleware readme example

[adamyala]

Thank you for the wonderful module! It saved me the trouble of having to reinvent the wheel.

Please let me know if a PR with the below change would be welcome.

Currently, the example in the README uses MIDDLEWARE_CLASSES. I believe this was the old setting for middleware and has been succeeded by MIDDLEWARE. I tested this module just now using MIDDLEWARE_CLASSES and I couldn't seem to get it working. I believe as of 1.10, MIDDLEWARE_CLASSES now has a different function https://docs.djangoproject.com/en/2.2/topics/http/middleware/#upgrading-pre-django-1-10-style-middleware
To avoid confusion, I'd like to suggest changing MIDDLEWARE_CLASSES in the readme to MIDDLEWARE.

[pcraston]

Hi there,

Sure makes sense, a PR updating the README would be great - let's show what's required both for pre-1.10 and post.1.10

Thanks!