www/py-django-auth-ldap: Update to 1.7.0

While I'm here:

• Pet portlint

Notable changes since 1.5.0:

• Add support for Python 3.7 and Django 2.1
• Fix group membership queries with DNs containing non-ascii characters on Python 2.7

https://github.com/django-auth-ldap/django-auth-ldap/blob/1.7.0/CHANGES

PR: 236051
Approved by: miwi (mentor), maintainer timeout
Differential Revision: https://reviews.freebsd.org/D19436