Write a function that takes the number of seconds and returns the digital format clock time as a string. Time should be counted from 00:00:00.
digitalClock(5025) ➞ "01:23:45"
// 5025 seconds is 1 hour, 23 mins, 45 secs.
digitalClock(61201) ➞ "17:00:01"
// No AM/PM. 24h format.
digitalClock(87000) ➞ "00:10:00"
// It's 00:10 next day.
seconds is always greater than or equal to 0.