doc: fix broken doc links (#13644)

Some broken doc links I saw when compiling with `cargo +stable doc
--no-deps --document-private-items --workspace --open`

crates/nu-command/src/charting/hashable_value.rs

@@ -2,7 +2,7 @@ use chrono::{DateTime, FixedOffset};
 use nu_protocol::{ShellError, Span, Value};
 use std::hash::{Hash, Hasher};
 
-/// A subset of [`Value`](crate::Value), which is hashable.
+/// A subset of [`Value`], which is hashable.
 /// And it means that we can put the value into something like
 /// [`HashMap`](std::collections::HashMap) or [`HashSet`](std::collections::HashSet) for further
 /// usage like value statistics.

crates/nu-command/src/system/run_external.rs

@@ -506,7 +506,7 @@ pub fn which(name: impl AsRef<OsStr>, paths: &str, cwd: &Path) -> Option<PathBuf
 }
 
 /// Returns true if `name` is a (somewhat useful) CMD internal command. The full
-/// list can be found at https://ss64.com/nt/syntax-internal.html
+/// list can be found at <https://ss64.com/nt/syntax-internal.html>
 fn is_cmd_internal_command(name: &str) -> bool {
     const COMMANDS: &[&str] = &[
         "ASSOC", "CLS", "ECHO", "FTYPE", "MKLINK", "PAUSE", "START", "VER", "VOL",