[ImgBot] Optimize images

*Total -- 1,253.99kb -> 1,110.55kb (11.44%)

/screenshot.png -- 555.34kb -> 488.79kb (11.98%)
/.github/screnshot.png -- 698.65kb -> 621.76kb (11.01%)

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

Author: ImgBotApp