input: Write a function to find the day with the highest temperature.
  assert highest_temp([30, 32, 35, 28, 31, 36, 33])==5
  assert highest_temp([25, 27, 29, 28, 30, 26, 31])==6
  assert highest_temp([40, 42, 41, 39, 38, 37, 36])==1
output: def highest_temp(temps):
      return temps.index(max(temps))