Update Yacht's config.json to include the second required solution source file (#693)

* Update Yacht's config.json to include the second required solution source file

* Put YachtCategory.kt file under a better file category in config

Author: IndiGan

exercises/practice/yacht/.meta/config.json

@@ -15,6 +15,9 @@
     ],
     "example": [
       ".meta/src/reference/kotlin/Yacht.kt"
+    ],
+    "editor": [
+      "src/main/kotlin/YachtCategory.kt"
     ]
   },
   "blurb": "Score a single throw of dice in the game Yacht.",