The `srcset` attribute isn't updated

[ZzZombo]

https://developer.mozilla.org/en-US/docs/Web/API/HTMLImageElement/srcset.

The generated HTML doesn't reflect the relative path to the file as it should, it remains as is.

[Jernik]

+1 this is blocking my use of httrack since it still hotlinks out to the original site. I'm going to try building it locally with this PR added:
#301