make test model django 3 compatible

src/django_deploy/tests/fake_app1/models.py

@@ -1,12 +1,13 @@
 # -*- coding: utf-8 -*-
 from __future__ import unicode_literals
 from django.db import models
-from django.utils.encoding import python_2_unicode_compatible
 
 
-@python_2_unicode_compatible
-class MyModel(models.Model):
+class MyModel(models.Model):  # pylint: disable=model-has-unicode
     chars = models.CharField(max_length=10)
 
     def __str__(self):
         return self.chars
+
+    def __unicode__(self):
+        return self.__str__()

tox.ini

@@ -1,10 +1,14 @@
 [tox]
-envlist = py3,py2
+envlist = py3-django3,py3-django2,py2-django1
 
 [testenv]
 deps = coverage
-       py2: pylint-django<2
-       py3: pylint-django
+       py2-django1: django<2
+       py2-django1: pylint-django<2
+       py3-django2: django<3
+       py3-django2: pylint-django
+       py3-django3: django
+       py3-django3: pylint-django
        pytest
        mock
 commands = coverage run -m pytest