[ImgBot] Optimize images

*Total -- 1,187.36kb -> 1,053.73kb (11.25%)

/screenshot.png -- 555.34kb -> 488.79kb (11.98%)
/.github/screnshot.png -- 632.02kb -> 564.94kb (10.61%)

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

Author: ImgBotApp