[ImgBot] Optimize images

*Total -- 343.95kb -> 298.22kb (13.29%)

/src/data/showcase/captcha-code.png -- 60.27kb -> 50.22kb (16.67%)
/docs/javascript/img/source.gif -- 283.68kb -> 248.00kb (12.58%)

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

Author: ImgBotApp