[ImgBot] Optimize images

*Total -- 731.20kb -> 511.84kb (30%)

/images/packet-loss.png -- 206.78kb -> 134.92kb (34.75%)
/images/global-selector.png -- 246.43kb -> 161.99kb (34.27%)
/images/mtr.png -- 188.99kb -> 127.13kb (32.73%)
/build/icon-256.png -- 14.98kb -> 14.77kb (1.4%)
/build/icon.png -- 37.01kb -> 36.51kb (1.35%)
/build/icon-512.png -- 37.01kb -> 36.51kb (1.35%)

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

Author: ImgBotApp