[ImgBot] Optimize images

*Total -- 49.13kb -> 21.88kb (55.46%)

/Snake Game/img/food.png -- 15.83kb -> 4.02kb (74.6%)
/Snake Game/img/ground.png -- 33.30kb -> 17.86kb (46.36%)

Signed-off-by: ImgBotApp <ImgBotHelp@gmail.com>

Author: ImgBotApp