fix: set example

src/data/question-groups/javascript/content/set.md

@@ -3,12 +3,15 @@ Set is another data structure in JavaScript which is similar to `Array` but the
 ```js
 const roadmap = new Set();
 roadmap.add('JavaScript');
+roadmap.add('JavaScript');
+
 roadmap.add('dynamic');
 roadmap.add(1995);
 
+console.log(roadmap.size); // 3, because the value 'JavaScript' is already present in the set
 console.log(roadmap.has('JavaScript')); // true
 
-roadmap.delete(1995);
+roadmap.delete('JavaScript');
-console.log(roadmap.has(1995)); // false
+console.log(roadmap.has('JavaScript')); // false
 console.log(roadmap.size); // 2
 ```