deprecation warnings

(venv) climu@titbet ~/osr/openstudyroom $ python -Wa manage.py
/home/climu/osr/venv/lib/python3.5/site-packages/wagtail/wagtailcore/models.py:17: RemovedInDjango20Warning: Importing from django.core.urlresolvers is deprecated in favor of django.urls.
  from django.core.urlresolvers import reverse
/home/climu/osr/venv/lib/python3.5/site-packages/wagtailmenus/models/menuitems.py:173: RemovedInDjango20Warning: on_delete will be a required arg for ParentalKey in Django 2.0. Set it to models.CASCADE on models and in existing migrations if you want to maintain the current default behavior. See https://docs.djangoproject.com/en/1.11/ref/models/fields/#django.db.models.ForeignKey.on_delete
  menu = ParentalKey('wagtailmenus.MainMenu', related_name="menu_items")
/home/climu/osr/venv/lib/python3.5/site-packages/wagtailmenus/models/menuitems.py:178: RemovedInDjango20Warning: on_delete will be a required arg for ParentalKey in Django 2.0. Set it to models.CASCADE on models and in existing migrations if you want to maintain the current default behavior. See https://docs.djangoproject.com/en/1.11/ref/models/fields/#django.db.models.ForeignKey.on_delete
  menu = ParentalKey('wagtailmenus.FlatMenu', related_name="menu_items")
/home/climu/osr/venv/lib/python3.5/site-packages/puput/models.py:111: RemovedInDjango20Warning: on_delete will be a required arg for ForeignKey in Django 2.0. Set it to models.CASCADE on models and in existing migrations if you want to maintain the current default behavior. See https://docs.djangoproject.com/en/1.11/ref/models/fields/#django.db.models.ForeignKey.on_delete
  verbose_name=_('Parent category'))
/home/climu/osr/venv/lib/python3.5/site-packages/puput/models.py:139: RemovedInDjango20Warning: on_delete will be a required arg for ForeignKey in Django 2.0. Set it to models.CASCADE on models and in existing migrations if you want to maintain the current default behavior. See https://docs.djangoproject.com/en/1.11/ref/models/fields/#django.db.models.ForeignKey.on_delete
  category = models.ForeignKey(Category, related_name="+", verbose_name=_('Category'))
/home/climu/osr/venv/lib/python3.5/site-packages/puput/models.py:140: RemovedInDjango20Warning: on_delete will be a required arg for ParentalKey in Django 2.0. Set it to models.CASCADE on models and in existing migrations if you want to maintain the current default behavior. See https://docs.djangoproject.com/en/1.11/ref/models/fields/#django.db.models.ForeignKey.on_delete
  page = ParentalKey('EntryPage', related_name='entry_categories')
/home/climu/osr/venv/lib/python3.5/site-packages/puput/models.py:147: RemovedInDjango20Warning: on_delete will be a required arg for ParentalKey in Django 2.0. Set it to models.CASCADE on models and in existing migrations if you want to maintain the current default behavior. See https://docs.djangoproject.com/en/1.11/ref/models/fields/#django.db.models.ForeignKey.on_delete
  content_object = ParentalKey('EntryPage', related_name='entry_tags')
/home/climu/osr/venv/lib/python3.5/site-packages/puput/models.py:159: RemovedInDjango20Warning: on_delete will be a required arg for ParentalKey in Django 2.0. Set it to models.CASCADE on models and in existing migrations if you want to maintain the current default behavior. See https://docs.djangoproject.com/en/1.11/ref/models/fields/#django.db.models.ForeignKey.on_delete
  entrypage_from = ParentalKey('EntryPage', verbose_name=_("Entry"), related_name='related_entrypage_from')
/home/climu/osr/venv/lib/python3.5/site-packages/puput/models.py:160: RemovedInDjango20Warning: on_delete will be a required arg for ParentalKey in Django 2.0. Set it to models.CASCADE on models and in existing migrations if you want to maintain the current default behavior. See https://docs.djangoproject.com/en/1.11/ref/models/fields/#django.db.models.ForeignKey.on_delete
  entrypage_to = ParentalKey('EntryPage', verbose_name=_("Entry"), related_name='related_entrypage_to')
/home/climu/osr/venv/lib/python3.5/site-packages/postman/models.py:270: RemovedInDjango20Warning: on_delete will be a required arg for ForeignKey in Django 2.0. Set it to models.CASCADE on models and in existing migrations if you want to maintain the current default behavior. See https://docs.djangoproject.com/en/1.11/ref/models/fields/#django.db.models.ForeignKey.on_delete
  sender = models.ForeignKey(settings.AUTH_USER_MODEL, related_name='sent_messages', null=True, blank=True, verbose_name=_("sender"))
/home/climu/osr/venv/lib/python3.5/site-packages/postman/models.py:271: RemovedInDjango20Warning: on_delete will be a required arg for ForeignKey in Django 2.0. Set it to models.CASCADE on models and in existing migrations if you want to maintain the current default behavior. See https://docs.djangoproject.com/en/1.11/ref/models/fields/#django.db.models.ForeignKey.on_delete
  recipient = models.ForeignKey(settings.AUTH_USER_MODEL, related_name='received_messages', null=True, blank=True, verbose_name=_("recipient"))
/home/climu/osr/venv/lib/python3.5/site-packages/postman/models.py:273: RemovedInDjango20Warning: on_delete will be a required arg for ForeignKey in Django 2.0. Set it to models.CASCADE on models and in existing migrations if you want to maintain the current default behavior. See https://docs.djangoproject.com/en/1.11/ref/models/fields/#django.db.models.ForeignKey.on_delete
  parent = models.ForeignKey('self', related_name='next_messages', null=True, blank=True, verbose_name=_("parent message"))
/home/climu/osr/venv/lib/python3.5/site-packages/postman/models.py:274: RemovedInDjango20Warning: on_delete will be a required arg for ForeignKey in Django 2.0. Set it to models.CASCADE on models and in existing migrations if you want to maintain the current default behavior. See https://docs.djangoproject.com/en/1.11/ref/models/fields/#django.db.models.ForeignKey.on_delete
  thread = models.ForeignKey('self', related_name='child_messages', null=True, blank=True, verbose_name=_("root message"))
/home/climu/osr/venv/lib/python3.5/site-packages/postman/models.py:285: RemovedInDjango20Warning: on_delete will be a required arg for ForeignKey in Django 2.0. Set it to models.CASCADE on models and in existing migrations if you want to maintain the current default behavior. See https://docs.djangoproject.com/en/1.11/ref/models/fields/#django.db.models.ForeignKey.on_delete
  null=True, blank=True, verbose_name=_("moderator"))