message: Fix doc link.
  The rust linkchecker does not like directory-style links.
diff: @@ -179,7 +179,7 @@ manifest is located.
  [cargo-unstable]: https://doc.rust-lang.org/nightly/cargo/reference/unstable.html
  [config option]: reference/config.html
  [directory layout]: reference/manifest.html#the-project-layout
  -[edition guide]: ../edition-guide/
  +[edition guide]: ../edition-guide/index.html
  [edition-field]: reference/manifest.html#the-edition-field-optional
  [environment variable]: reference/environment-variables.html
  [feature]: reference/manifest.html#the-features-section
  