[ImgBot] Optimize images

*Total -- 1,228.64kb -> 1,099.15kb (10.54%)

/assets/cn/crawler.png -- 93.31kb -> 22.16kb (76.25%)
/assets/en/crawler.png -- 60.48kb -> 15.89kb (73.74%)
/assets/en/crawler-result.png -- 623.25kb -> 613.97kb (1.49%)
/assets/cn/crawler-result.png -- 451.60kb -> 447.14kb (0.99%)

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

Author: ImgBotApp