[ImgBot] Optimize images

*Total -- 547.36kb -> 524.57kb (4.16%)

/pkgdown/favicon/favicon.svg -- 16.53kb -> 0.03kb (99.83%)
/img/README-example-2.png -- 99.89kb -> 97.80kb (2.09%)
/vignettes/country-1.png -- 49.11kb -> 48.26kb (1.73%)
/img/README-example-1.png -- 110.84kb -> 109.35kb (1.35%)
/vignettes/giscoR-1.png -- 146.66kb -> 145.14kb (1.03%)
/pkgdown/favicon/apple-touch-icon-152x152.png -- 4.49kb -> 4.47kb (0.48%)
/pkgdown/favicon/apple-touch-icon-180x180.png -- 5.21kb -> 5.19kb (0.37%)
/pkgdown/favicon/web-app-manifest-512x512.png -- 35.35kb -> 35.22kb (0.36%)
/img/README-labels-1.png -- 79.28kb -> 79.11kb (0.21%)

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

Author: ImgBotApp