Fix std links that have digits in them.

Author: ehuss

mdbook-spec/src/main.rs

@@ -25,7 +25,7 @@ static ADMONITION_RE: Lazy<Regex> = Lazy::new(|| {
 /// the standard library using rustdoc's intra-doc notation.
 const STD_LINK: &str = r"(?: [a-z]+@ )?
                          (?: std|core|alloc|proc_macro|test )
-                         (?: ::[A-Za-z_!:<>{}()\[\]]+ )?";
+                         (?: ::[A-Za-z0-9_!:<>{}()\[\]]+ )?";
 
 /// The Regex for a markdown link that might be a link to the standard library.
 static STD_LINK_RE: Lazy<Regex> = Lazy::new(|| {