Django 1.8: django.contrib.admin.util is deprecated

[coredumperror]

In Django 1.8, django-inspectional-registration's use of django.contrib.admin.util triggers a deprecation warning. Instead, registration/admin/__init__.py should be using django.contrib.admin.utils (notice the "s" at the end.

Since this is a one-character fix, I figured doing a pull request was overkill. The only place this needs to be fixed is registration/admin/__init__.py.

[lambdalisue]

Thanks for reporting. Well it is not actually one-character fix thus could you confirm #46

[coredumperror]

Oh right, you need to worry about being compatible with older Django versions. I wouldn't have even thought of that, so a pull request from me would have been deceptively incomplete.

That change looks great to me.

[lambdalisue]

Ok, I'll merge it