change example element of multidimensional array

When teaching this subject I found that an example where you can see for which array the first and the second value in the [] after matrix stand, helps understanding better.

Author: sneeed

1-js/05-data-types/04-array/article.md

@@ -426,7 +426,7 @@ let matrix = [
   [7, 8, 9]
 ];
 
-alert( matrix[1][1] ); // 5, the central element
+alert( matrix[0][1] ); // 2, the second value of the first inner array
 ```
 
 ## toString