tox: Update a text constant for grep

mesage ID seems to have changed

Author: atodorov

tox.ini

@@ -17,7 +17,7 @@ requires =
 
 [testenv]
 commands =
-    django_not_installed: bash -c \'pylint --load-plugins=pylint_django setup.py | grep django-not-available\'
+    django_not_installed: bash -c \'pylint --load-plugins=pylint_django setup.py | grep django-not-configured\'
     django_is_installed: pylint --load-plugins=pylint_django --disable=E5110 setup.py
     flake8: flake8
     pylint: pylint --rcfile=tox.ini -d missing-docstring,too-many-branches,too-many-return-statements,too-many-ancestors,fixme --ignore=tests pylint_django setup