remove app config from __init__.py; lint fix

Author: kseever

simple_history/tests/__init__.py

@@ -1 +0,0 @@
-default_app_config = 'simple_history.tests.apps.TestsConfig'

simple_history/tests/tests/test_models.py

@@ -1054,6 +1054,7 @@ def test_changed_value_lost(self):
         instance = historical.instance
         self.assertEqual(instance.place, new_place)
 
+
 def add_static_history_ip_address(sender, **kwargs):
     history_instance = kwargs['history_instance']
     history_instance.ip_address = '192.168.0.1'