input: Write a python function to determine the winner in a rock, paper, scissors game.
  assert check_winner('rock', 'scissors') == 'You won!'
  assert check_winner('paper', 'rock') == 'You won!'
  assert check_winner('scissors', 'paper') == 'You won!'
  assert check_winner('rock', 'rock') == 'Draw'
  assert check_winner('paper', 'paper') == 'Draw'
  assert check_winner('scissors', 'scissors') == 'Draw'
  assert check_winner('rock', 'paper') == 'Computer won!'
  assert check_winner('paper', 'scissors') == 'Computer won!'
  assert check_winner('scissors', 'rock') == 'Computer won!'
output: def check_winner(player, computer):
      if player == computer:
          return 'Draw'
      elif (player == 'rock' and computer == 'scissors') or \
           (player == 'paper' and computer == 'rock') or \
           (player == 'scissors' and computer == 'paper'):
          return 'You won!'
      else:
          return 'Computer won!'