Fix link typo in 1.20.0 release notes

Author: WiSaGaN

RELEASES.md

@@ -170,7 +170,7 @@ Compatibility Notes
 [`slice::sort_unstable_by_key`]: https://doc.rust-lang.org/std/primitive.slice.html#method.sort_unstable_by_key
 [`slice::sort_unstable_by`]: https://doc.rust-lang.org/std/primitive.slice.html#method.sort_unstable_by
 [`slice::sort_unstable`]: https://doc.rust-lang.org/std/primitive.slice.html#method.sort_unstable
-[`ste::from_boxed_utf8_unchecked`]: https://doc.rust-lang.org/std/str/fn.from_boxed_utf8_unchecked.html
+[`str::from_boxed_utf8_unchecked`]: https://doc.rust-lang.org/std/str/fn.from_boxed_utf8_unchecked.html
 [`str::as_bytes_mut`]: https://doc.rust-lang.org/std/primitive.str.html#method.as_bytes_mut
 [`str::from_utf8_mut`]: https://doc.rust-lang.org/std/str/fn.from_utf8_mut.html
 [`str::from_utf8_unchecked_mut`]: https://doc.rust-lang.org/std/str/fn.from_utf8_unchecked_mut.html