Support chrome webp images format

[samized]

Hi,

Thanks for this great chrome extension.

If the website uses the webp images format with chrome, there will be no images in the ebook. I think the backend is not able to fetch this type of image.

Example page: https://www.republik.ch/2018/07/24/zimbabwes-geschichte-zeigt-ein-duesteres-bild

Example url from chrome: https://cdn.republik.space/s3/republik-assets/github/republik/article-zimbabwe-und-der-hoellenhund/images/28f7748f4e791665e88a0a324c212fc3c8d72a2b.jpeg.webp?size=3600x2328&resize=3000x

Same image when using firefox: https://cdn.republik.space/s3/republik-assets/github/republik/article-zimbabwe-und-der-hoellenhund/images/28f7748f4e791665e88a0a324c212fc3c8d72a2b.jpeg?size=3600x2328&resize=3000x

My workaround for now is to use firefox for epub generation.

[haroldtreen]

Interesting! Might be a matter of adding webp as a known filetype: https://github.com/haroldtreen/epub-press/blob/master/lib/constants.js#L3 ...