Django 1.8 compatibility

`transaction.commit_on_success` and `Options.module_name` are deprecated in Django 1.7 and will be removed in 1.8
If you look in the Travis output, this line causes an error on Django 1.8.  This is because the third parameter to getattr() is evaluated whether 'atomic' is found or not, and django.db.transaction.commit_on_success doesn't exist in 1.8.

Perhaps:
```python
atomic_decorator = getattr(django.db.transaction, 'atomic') or getattr(django.db.transaction, 'commit_on_success')
```