Suspicious URL pattern warning during deployment

[zhiltsov-max]

The problem
Documented installation steps for Ubuntu 18.04 produce the following warning message during the deployment.

How to reproduce

$ docker-compose build
$ docker-compose up -d
$ docker exec -it cvat bash -ic 'python3 ~/manage.py createsuperuser'

System check identified some issues:

WARNINGS:
?: (2_0.W001) Your URL pattern 'api/swagger.<slug:format>$' [name='schema-json'] has a route that contains '(?P<', begins with a '^', or ends with a '$'. This was likely an oversight when migrating to django.urls.path().
Username (leave blank to use 'django'):

Environment

• OS: Ubuntu 18.04
• Commit SHA: f537236

[nmanovic]

It should be fixed by #978