run black over stubs, add checking to travis

django-stubs-generated/core/management/commands/shell.pyi

@@ -3,7 +3,6 @@ from typing import Any, Dict, Optional, Union
 from django.core.management import BaseCommand
 from django.core.management.base import CommandParser
 
-
 class Command(BaseCommand):
     stderr: django.core.management.base.OutputWrapper
     stdout: django.core.management.base.OutputWrapper