Correct sorting example for Ordering in scaladoc

### Sorting example for Ordering in scaladoc corrected


Ordering example code for
```scala
Sorting.quickSort(pairs)(Ordering.by[(String, Int, Int), Int](_._2)
```

should be fixed like below    
```scala
Sorting.quickSort(pairs)(Ordering.by[(String, Int, Int), Int](_._2))
```