[ImgBot] optimizes images (#3175)

*Total -- 989.43kb -> 562.65kb (43.13%)

/assets/mocha-banner-192.png -- 15.30kb -> 6.35kb (58.49%)
/docs/images/emacs.png -- 591.08kb -> 280.32kb (52.58%)
/docs/images/reporter-dot.png -- 13.15kb -> 7.28kb (44.63%)
/docs/images/jetbrains-plugin.png -- 87.05kb -> 50.34kb (42.17%)
/docs/images/wallaby.png -- 47.87kb -> 33.00kb (31.06%)
/assets/mocha-logo-128.png -- 7.27kb -> 5.19kb (28.62%)
/assets/mocha-logo-192.png -- 10.13kb -> 7.25kb (28.45%)
/docs/images/mocha_side_bar.png -- 214.39kb -> 170.27kb (20.58%)
/assets/mocha-logo-64.png -- 3.20kb -> 2.65kb (17.01%)

Author: ImgBotApp