config.json in trackler-2.0.6.30

- old
+ new

@@ -183,12 +183,14 @@
         "Maps",
         "Strings"
       ]
     },
     {
-      "difficulty": 1,
+      "difficulty": 3,
       "slug": "parallel-letter-frequency",
-      "topics": []
+      "topics": [
+        "Concurrency"
+      ]
     },
     {
       "difficulty": 1,
       "slug": "sum-of-multiples",
       "topics": []