Update article.md

How about adding semicolon like this?
Yes, omitting the semicolon does not cause a problem. But in this
case, adding the semicolon is more consistent and obvious.

Author: jooohyun

1-js/05-data-types/05-array-methods/article.md

@@ -329,7 +329,7 @@ It calls the function for each element of the array and returns the array of res
 For instance, here we transform each element into its length:
 
 ```js run
-let lengths = ["Bilbo", "Gandalf", "Nazgul"].map(item => item.length)
+let lengths = ["Bilbo", "Gandalf", "Nazgul"].map(item => item.length);
 alert(lengths); // 5,7,6
 ```