[1.8.x] Replaced deprecated requires_model_validation in docs.
[1.8.x] Replaced deprecated requires_model_validation in docs.

Backport of 18192b9fa4387d5e6c677a7929d91ce04f92cda7 from master

pquentin/django,pquentin/django,pquentin/django,h4r5h1t/django-hauthy,h4r5h1t/django-hauthy,h4r5h1t/django-hauthy,h4r5h1t/django-hauthy