fix(challenges): commented output was wrong

challenges/02-javascript-algorithms-and-data-structures/es6.json

@@ -562,7 +562,7 @@
             "  };",
             "})();",
             "console.log(increment(5, 2)); // returns 7",
-            "console.log(increment(5)); // returns NaN"
+            "console.log(increment(5)); // returns 6"
           ],
           "head": [],
           "tail": []