input: Write a python function to round a number to a given number of decimal places.
  assert round_number(2.6789, 2) == 2.68
  assert round_number(5.12345, 3) == 5.123
  assert round_number(10.987654, 4) == 10.9877
output: def round_number(number, decimal_places):
      return round(number, decimal_places)