community/pngquant: upgrade to 3.0.3 & libimagequant to 4.2.2
https://github.com/kornelski/pngquant/compare/3.0.1...3.0.3
https://github.com/ImageOptim/libimagequant/blob/4.2.2/CHANGELOG
https://github.com/ImageOptim/libimagequant/compare/4.1.0...4.2.2
9f15d1c53938a441a6bbfb2de866492797f69e22 is libimagequant 4.1.0