www/py-django-auth-ldap: Update to 2.1.0

Changelog:

• Reject authentication requests without a username
• Added support for Django 3.0 and Python 3.8
• Removed support for Django 2.1 which is End-of-Life

https://github.com/django-auth-ldap/django-auth-ldap/blob/2.1.0/CHANGES