Fix snapshot diff update issue

nummi/main/models.py

@@ -122,6 +122,13 @@ class Snapshot(models.Model):
             self.diff = self.value - self.previous.value
         super().save(*args, **kwargs)
 
+        try:
+            _next = self.__class__.objects.get(previous=self)
+        except self.__class__.DoesNotExist:
+            pass
+        else:
+            _next.save(only_super=True)
+
     def delete(self, *args, only_super=False, **kwargs):
         if not only_super:
             try: