fix question details: JavaScript, ES6 category (#17407)

* fix question details

* Update es6.json

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

@@ -823,7 +823,7 @@
             "  \"use strict\";",
             "  // change code below this line",
             "  arr = list; // change this",
-            "  // change code below this line",
+            "  // change code above this line",
             "  return arr;",
             "}",
             "const arr = removeFirstTwo(source);",
@@ -1384,4 +1384,4 @@
       }
     }
   ]
-}
+}