Fix rustdoc::bare_urls lint in lexical code

    warning: this URL is not a hyperlink
     --> src/lexical/errors.rs:9:9
      |
    9 | //!     https://golang.org/src/strconv/atof.go
      |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use an automatic link instead: `<https://golang.org/src/strconv/atof.go>`
      |
      = note: bare URLs are not automatically turned into clickable links
      = note: `#[warn(rustdoc::bare_urls)]` on by default

src/lexical/errors.rs

@@ -5,8 +5,7 @@
 //! This estimates the error in a floating-point representation.
 //!
 //! This implementation is loosely based off the Golang implementation,
-//! found here:
-//!     https://golang.org/src/strconv/atof.go
+//! found here: <https://golang.org/src/strconv/atof.go>
 
 use super::float::*;
 use super::num::*;