Update article.md

Author: leviding

1-js/05-data-types/08-weakmap-weakset/article.md

@@ -30,7 +30,7 @@ let array = [ john ];
 john = null; // overwrite the reference
 
 *!*
-// the object previously referenced by john is stored inside the array 
+// the object previously referenced by john is stored inside the array
 // therefore it won't be garbage-collected
 // we can get it as array[0]
 */!*