Fixed dependency for python-dateutil

[mcrot]

Hi, I'm interested in using django-statsy in my Django project and I would like to try it. After adding it to my requirements, I've problems to resolve my dependencies, because the version of python-dateutil is fixed here: https://github.com/zhebrak/django-statsy/blob/d74845e75c78842fc3890db123ab6e36fe2d3973/requirements.txt#L4

Is this still necessary? And since the project has not been updated for some time: Are there any objections using it with Django 2.2?