Rename AppConfig classname to remain consistent with its app name

The Django app name is `postgres hot upgrade`, not update.

Author: wo0dyn

Diff for: django_postgres_hot_upgrade/__init__.py

@@ -1 +1 @@
-default_app_config = "django_postgres_hot_upgrade.app.PostgresHotUpdateConfig"
+default_app_config = "django_postgres_hot_upgrade.app.PostgresHotUpgradeConfig"

Diff for: django_postgres_hot_upgrade/app.py

@@ -24,7 +24,7 @@ def _on_connect(connection, **kwargs):
         _version_cache[connection.alias] = version
 
 
-class PostgresHotUpdateConfig(AppConfig):
+class PostgresHotUpgradeConfig(AppConfig):
 
     name = "django_postgres_hot_upgrade"