[ImgBot] Optimize images

*Total -- 18.38kb -> 9.27kb (49.53%)

/screenshots/screenshots4.png -- 4.69kb -> 2.12kb (54.84%)
/screenshots/screenshots3.png -- 5.43kb -> 2.45kb (54.83%)
/screenshots/screenshots5.png -- 2.22kb -> 1.04kb (53.19%)
/screenshots/screenshots2.png -- 3.42kb -> 2.07kb (39.62%)
/screenshots/screenshots.png -- 2.62kb -> 1.60kb (38.88%)

Author: ImgBotApp