wrong doc generated when using ModelViewSets

When using ModelViewSets, the apis shown in doc are wrong.

``` python
class UserInfoSerializer(ModelSerializer):
class Meta:
model = User

class UserInfo(ModelViewSet):
queryset = User.objects.all()
serializer_class = UserInfoSerializer

urlpatterns = [
url(r'^docs/', include('rest_framework_docs.urls')),
]

urlpatterns += router.urls
```

The results in `/docs/` are

```
/docs/users/ OPTIONS
/docs/users// OPTIONS
```

Is this a already known bug?

Start by reproducing the ModelViewSet example and inspect how the documentation generator derives endpoints from router URLs. Compare the generated /docs/ entries with the routes exposed by the viewset; done means the documentation lists the correct ModelViewSet operations instead of only OPTIONS endpoints.

Written by the indexing model from the issue text.