Add instruction to use var for declaring variables

[jinolacson]

javascript-4-prototype/arrayProperty.js

Lines 1 to 5 in e8c19e3

	//Just like you can add methods to your own constructor, you can also add methods and properties to built in classes in JavaScript like Arrays and Objects.
	//Add a reverse method to the String 'class' so that every instance of String can call reverse and reverse itself.
	//code here

Change into:

//Note: use var for declaring variables
//Just like you can add methods to your own constructor, you can also add methods and properties to built in classes in JavaScript like Arrays and Objects.

//Add a reverse method to the String 'class' so that every instance of String can call reverse and reverse itself.
  
  //code here