[ImgBot] Optimize images

*Total -- 1,253.20kb -> 1,109.73kb (11.45%)

/screenshot.png -- 555.34kb -> 488.79kb (11.98%)
/.github/screnshot.png -- 697.86kb -> 620.95kb (11.02%)

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

Author: ImgBotApp