Update Exercise13_02.java

[amralgendi]

Fixed limit of Random.nextInt()

[shreyashHake]

It can also be
int randInx = new Random().nextInt(100);
as the initial size is 100 specified at line 17,
which is eventually same to list.size() as Random(n) -> gives value from (0 to n -1).

[HarryDulaney]

Nice! Yea, in this case, I like using list.size(). The shuffle(ArrayList list) method is more flexible to different-sized inputs that way. Thank you for your contributions!