Use "del" instead of "delete" for batch deletion in MobileLevelImpl.mm

ios/Plugin/MobileLevelImpl.mm

@@ -197,7 +197,7 @@ NSDictionary * EMPTY_SUCCESS = nil;
         
         if ([type isEqualToString:@"put"]) {
             batch.Put(decoded_key, decoded_value);
-        } else if ([type isEqualToString:@"delete"]) {
+        } else if ([type isEqualToString:@"del"]) {
             batch.Delete(decoded_key);
         }
     }