Merge pull request #133 from ractf/hotfix/cache-invalidation

Invalidate challenge cache when a challenge is deleted.

src/challenge/signals.py

@@ -1,11 +1,11 @@
 from django.core.cache import caches
-from django.db.models.signals import post_save
+from django.db.models.signals import post_save, post_delete
 from django.dispatch import receiver
 
 from challenge.models import Challenge
 
 
-@receiver(post_save, sender=Challenge)
-def challenge_save(sender, instance, **kwargs):
+@receiver([post_save, post_delete], sender=Challenge)
+def challenge_cache_invalidate(sender, instance, **kwargs):
     new_index = caches["default"].get("challenge_mod_index", 0) + 1
     caches["default"].set("challenge_mod_index", new_index)