Fix CI.

oj/__init__.py

@@ -3,4 +3,4 @@ from __future__ import absolute_import, unicode_literals
 # Django starts so that shared_task will use this app.
 from .celery import app as celery_app
 
-__all__ = ['celery_app']
+__all__ = ["celery_app"]

oj/celery.py

@@ -3,15 +3,15 @@ import os
 from celery import Celery
 from django.conf import settings
 
-# set the default Django settings module for the 'celery' program.
-os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'oj.settings')
+# set the default Django settings module for the "celery" program.
+os.environ.setdefault("DJANGO_SETTINGS_MODULE", "oj.settings")
 
 
-app = Celery('oj')
+app = Celery("oj")
 
 # Using a string here means the worker will not have to
 # pickle the object when using Windows.
-app.config_from_object('django.conf:settings')
+app.config_from_object("django.conf:settings")
 
 # load task modules from all registered Django app configs.
 app.autodiscover_tasks(lambda: settings.INSTALLED_APPS)