[ImgBot] Optimize images

*Total -- 1,222.98kb -> 1,081.11kb (11.6%)

/screenshot.png -- 555.34kb -> 488.79kb (11.98%)
/.github/screnshot.png -- 667.64kb -> 592.33kb (11.28%)

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

Author: ImgBotApp