Fix incompatibility with Django 2.1 and jQuery 3

[kikeh]

As Django 2.1 upgrades jQuery from 2.2.3 to 3.3.1, in which the attribute selector is removed, the sortable script stopped updating the order of the elements. I have added the compatibility proposed by jQuery in its deprecation note in the documentation.

[iMakedonsky]

Thanks for this patch. Already using your version via pip install https://github.com/kikeh/django-suit/tarball/v2