Given a number, return a list containing the two halves of the number. If the number is odd, make the rightmost number higher.
numberSplit(25) ➞ [12, 13]
numberSplit(4) ➞ [2, 2]
numberSplit(10) ➞ [5, 5]
numberSplit(11) ➞ [5, 6]
numberSplit(-9) ➞ [-5, -4]