Switch to short form for serde.rs link in rustdoc
Switch to short form for serde.rs link in rustdoc

Fixes a rustdoc warning:

    warning: unneeded long form for URL
      --> serde/src/lib.rs:12:27
       |
    12 | //! See the Serde website [https://serde.rs/] for additional documentation and
       |                           ^^^^^^^^^^^^^^^^^^^ help: use an automatic link instead: `<https://serde.rs/>`
       |
       = note: `#[warn(non_autolinks)]` on by default

serde-rs/serde