[ImgBot] Optimize images

*Total -- 196.55kb -> 124.91kb (36.45%)

/stars/star2.png -- 18.57kb -> 11.33kb (39.02%)
/stars/star5.png -- 16.79kb -> 10.25kb (38.98%)
/stars/star3.png -- 21.92kb -> 13.78kb (37.15%)
/stars/star8.png -- 23.51kb -> 14.89kb (36.67%)
/stars/star4.png -- 26.65kb -> 17.09kb (35.87%)
/stars/star6.png -- 32.26kb -> 20.82kb (35.46%)
/stars/star7.png -- 31.18kb -> 20.13kb (35.44%)
/stars/star1.png -- 25.67kb -> 16.63kb (35.21%)

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

Author: ImgBotApp