[ImgBot] Optimize images

*Total -- 1,738.38kb -> 1,346.10kb (22.57%)

/courses/github/img-17.png -- 67.17kb -> 43.38kb (35.42%)
/courses/github/img-5.png -- 77.95kb -> 52.04kb (33.24%)
/courses/github/img-15.png -- 82.89kb -> 55.71kb (32.79%)
/courses/github/img-11.png -- 69.38kb -> 47.49kb (31.55%)
/courses/github/img-4.png -- 69.50kb -> 48.18kb (30.68%)
/courses/github/img-14.png -- 71.78kb -> 50.04kb (30.28%)
/courses/github/img-12.png -- 58.94kb -> 41.87kb (28.97%)
/courses/github/img-16.png -- 92.45kb -> 65.95kb (28.66%)
/courses/github/img-13.png -- 50.49kb -> 36.91kb (26.9%)
/courses/github/img-2.png -- 182.45kb -> 141.36kb (22.52%)
/courses/github/img-1.png -- 223.25kb -> 176.87kb (20.78%)
/courses/github/img-10.png -- 107.85kb -> 89.62kb (16.9%)
/courses/github/img-8.png -- 133.03kb -> 111.44kb (16.23%)
/courses/github/img-7.png -- 134.04kb -> 112.30kb (16.22%)
/courses/github/img-9.png -- 135.08kb -> 113.36kb (16.08%)
/courses/github/img-3.png -- 41.31kb -> 34.83kb (15.68%)
/courses/github/img-6.png -- 140.84kb -> 124.74kb (11.43%)

Signed-off-by: ImgBotApp <[email protected]>

Author: ImgBotApp