fix(challenges): change comment to make it clearer which lines to edit

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

@@ -906,7 +906,7 @@
             "  \"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);",