message: Fix broken url in diagnostic.
diff: @@ -171,7 +171,7 @@ your `Cargo.toml` and then rerun this command. Once all warnings have been fixed
  then you can re-enable the `edition` key in `Cargo.toml`. For some more
  information about transitioning to the {0} edition see:
  - https://rust-lang-nursery.github.io/edition-guide/editions/transitioning.html
  + https://rust-lang-nursery.github.io/edition-guide/editions/transitioning-your-code-to-a-new-edition.html
  ",
  edition,
  file,
  