[ImgBot] Optimize images

*Total -- 368.03kb -> 322.12kb (12.48%)

/assets/en/crawler.png -- 39.29kb -> 8.47kb (78.44%)
/assets/cn/crawler.png -- 52.81kb -> 40.83kb (22.69%)
/assets/cn/crawler-result.png -- 142.13kb -> 140.50kb (1.15%)
/assets/en/crawler-result.png -- 133.80kb -> 132.32kb (1.1%)

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

Author: ImgBotApp