[ImgBot] Optimize images

*Total -- 1,190.29kb -> 1,051.69kb (11.64%)

/screenshot.png -- 555.34kb -> 488.79kb (11.98%)
/.github/screnshot.png -- 634.95kb -> 562.90kb (11.35%)

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

Author: ImgBotApp