[ImgBot] Optimize images (#19)

*Total -- 1,751.70kb -> 1,586.78kb (9.41%)

/assets/poster/w12.jpg -- 1,157.99kb -> 1,035.21kb (10.6%)
/assets/poster/w6.jpg -- 593.71kb -> 551.58kb (7.1%)

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

Co-authored-by: ImgBotApp <ImgBotHelp@gmail.com>

Author: imgbot[bot]