Fix cheat test

[evanthegrayt]

The cheating isn't actually being tested properly. This...

    game = RoShamBo.new(cheater: :user)
    50.times do
      game.play(:rock) until game.over?
      assert_equal(:user, game.winner)
    end

...should be...

    50.times do
      game = RoShamBo.new(cheater: :user)
      game.play(:rock) until game.over?
      assert_equal(:user, game.winner)
    end