Uno game: fix wild card color assignment; fix typos

[kaiks]

Right now the wild card color gets assigned randomly when it gets drawn from the deck:

        # draw a wild card
        if card.type == 'wild':
            card.color = self.np_random.choice(UnoCard.info['color'])

and the player is then able to pick any wild card color:

                        if wild_flag == 0:
                            wild_flag = 1
                            legal_actions.extend(WILD)

however, whatever color the player picks, the original random card color gets played. This PR fixes the problem by changing the card color during action execution.

This also makes the dqn training more effective against the random agent. Previous results:

0 experiments/uno_dqn_result/model.pth 0.0174
1 random -0.0174

After the change:

--> Running on the CPU
0 experiments/uno_dqn_result/model.pth 0.0294
1 random -0.0294

[daochenzha]

@kaiks LGTM! Thank you for the fix!