Spiral matrix : add topics (#956)

* '#925-addTopics'

* added topic for spiral-matrix

* added topic for spiral-matrix

* Update config.json

config.json

       "core": false,
       "difficulty": 6,
       "slug": "spiral-matrix",
-      "topics": null,
+      "topics": [
+        "loops",
+        "arrays",
+        "integers",
+        "mathematics",
+        "matrices"
+      ],
       "unlocked_by": "matrix",
       "uuid": "163fcc6b-c054-4232-a88b-0aded846a6eb"
     },