input: Write a python function to compute the sum of each row in a matrix.
  assert rowSum([[1, 2, 3], [4, 5, 6], [7, 8, 9]]) == [6, 15, 24]
  assert rowSum([[0, 0, 0], [0, 0, 0], [0, 0, 0]]) == [0, 0, 0]
  assert rowSum([[1, -1, 1], [-1, 1, -1], [1, -1, 1]]) == [1, -1, 1]
output: def rowSum(matrix):
      return [sum(row) for row in matrix]