Update dependencies for security vulnerabilities

pipfile.lock and requirements.txt need the following change applied:
django>=2.0.8

CVE-2018-14574
moderate severity
Vulnerable versions: >= 2.0, < 2.0.8
Patched version: 2.0.8
django.middleware.common.CommonMiddleware in Django 1.11.x before 1.11.15 and 2.0.x before 2.0.8 has an Open Redirect.

CVE-2018-6188
moderate severity
Vulnerable versions: >= 2.0.0, < 2.0.2
Patched version: 2.0.2
django.contrib.auth.forms.AuthenticationForm in Django 2.0 before 2.0.2, and 1.11.8 and 1.11.9, allows remote attackers to obtain potentially sensitive information by leveraging data exposure from the confirm_login_allowed() method, as demonstrated by discovering whether a user account is inactive.

Start by inspecting pipfile.lock and requirements.txt to see how Django is pinned. Update the dependency requirement to Django >=2.0.8, then run the repository's tests to verify the demo application still works. Done means both dependency files no longer permit the vulnerable Django versions.

Written by the indexing model from the issue text.