input: Write a function to calculate "nth" root of a number.
  assert abs(root(625, 4) - 5) < 0.001
  assert abs(root(16, 2) - 4) < 0.001
  assert abs(root(27, 3) - 3) < 0.001
output: def root(number, n):
      return number ** (1 / n)