Fix pivot choice in QuickSort

Currently, QuickSort contains a bug in choice of pivot and the tests do not pick it up. Fix tests and then fix code.

https://github.com/all3fox/algos-java/blob/f43165ff0a573e4197695a48ca934829fb9c8f27/src/main/java/io/github/all3fox/sort/QuickSort.java#L25