Create a function that takes any nonnegative number as an argument and return it with it's digits in descending order. Descending order is when you sort from highest to lowest.
sortDescending(123) ➞ 321
sortDescending(1254859723) ➞ 9875543221
sortDescending(73065) ➞ 76530
You can expect non-negative numbers for all test cases.