[ImgBot] Optimize images

*Total -- 29.01kb -> 27.42kb (5.46%)

/documentation/coc-wordpress-backend.png -- 2.53kb -> 0.99kb (60.75%)
/coc/assets/images/logobubble.jpg -- 10.37kb -> 10.35kb (0.26%)
/coc/assets/images/coc-placeholder.jpg -- 16.10kb -> 16.08kb (0.13%)

Author: ImgBotApp