[ImgBot] Optimize images

[imgbot[bot]]

Beep boop. Your images are optimized!

Your image file size has been reduced by 12% 🎉

Details

File	Before	After	Percent reduction
/images/git_repo.png	94.25kb	68.81kb	26.99%
/images/color_schemes.png	160.51kb	128.95kb	19.66%
/images/hadley.png	115.36kb	100.82kb	12.60%
/slides.png	36.29kb	33.35kb	8.10%
/images/color_palette.png	58.92kb	55.68kb	5.50%
/images/chang_book.png	213.24kb	210.05kb	1.50%
Total :	678.58kb	597.66kb	11.92%

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