URI targets in TOC links have an extra slash

[triplingual]

The URIs in links.md are listed as
[0000]: {{ site.cookbook_url | absolute_url }}/recipe/[directory] "[Recipe title]"

Either the processing or the variable value for the template is making them come out in the TOC link targets as
http://preview.iiif.io//recipe/[directory]/
with an extra slash between the domain and the recipe directory. My Firefox on Mac handles it fine, but that's not to say that all browser/OS combos out there do, and besides it's also not accurate.

At this moment, I don't think I have an opinion on the "right" way to fix it — the processing changes, the links.md content changes, or something else entirely.