The retina image is not included in the API response so I am assuming a ${filename}_2x${extension} version of the image exists. If it fails to download, we default to the non-retina version.
Note that this will only apply to images that have not yet been downloaded. I also added a helper so that we don't attempt to download retina images on old comics that don't have one. I scrolled through xkcd.com and found that retina versions started with https://xkcd.com/1053/.
Fixes https://github.com/paulrehkugler/xkcd/issues/68.
The retina image is not included in the API response so I am assuming a
${filename}_2x${extension}version of the image exists. If it fails to download, we default to the non-retina version.Note that this will only apply to images that have not yet been downloaded. I also added a helper so that we don't attempt to download retina images on old comics that don't have one. I scrolled through xkcd.com and found that retina versions started with https://xkcd.com/1053/.