[ImgBot] Optimize images

*Total -- 1,218.87kb -> 1,076.31kb (11.7%)

/screenshot.png -- 555.34kb -> 488.79kb (11.98%)
/.github/screnshot.png -- 663.53kb -> 587.52kb (11.46%)

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

Author: ImgBotApp