std::r#try! - avoid link to nightly docs

Use a relative link to the current version of rust-by-example rather than
sending people to the nightly version.

Author: DanielEScherzer

library/core/src/macros/mod.rs

@@ -445,7 +445,7 @@ macro_rules! matches {
 /// [raw-identifier syntax][ris]: `r#try`.
 ///
 /// [propagating-errors]: https://doc.rust-lang.org/book/ch09-02-recoverable-errors-with-result.html#a-shortcut-for-propagating-errors-the--operator
-/// [ris]: https://doc.rust-lang.org/nightly/rust-by-example/compatibility/raw_identifiers.html
+/// [ris]: ../rust-by-example/compatibility/raw_identifiers.html
 ///
 /// `try!` matches the given [`Result`]. In case of the `Ok` variant, the
 /// expression has the value of the wrapped value.