Fixed code to match comments

Comments on lines 53 and 54 make me think that the program prints something as output, which obviously wasn't the case in the provisous version. I've added the calls to "println" which are necessary to match the corresponding comments.

Author: Sal Borrelli

_tour/traits.md

@@ -50,8 +50,8 @@ class IntIterator(to: Int) extends Iterator[Int] {
 
 
 val iterator = new IntIterator(10)
-iterator.next()  // prints 0
-iterator.next()  // prints 1
+println(iterator.next())  // prints 0
+println(iterator.next())  // prints 1
 ```
 This `IntIterator` class takes a parameter `to` as an upper bound. It `extends Iterator[Int]` which means that the `next` method must return an Int.