Update config.json

added topics for the queen-attack problem

config.json

       "core": false,
       "difficulty": 6,
       "slug": "queen-attack",
-      "topics": null,
+      "topics": [
+        "arrays",
+        "matrices",
+        "conditionals",
+        "mathematics",
+      ],
       "unlocked_by": "scrabble-score",
       "uuid": "5404109e-3ed9-4691-8eaf-af8b36024a44"
     },