Fix typos in 1.20 release notes

RELEASES.md

@@ -92,7 +92,7 @@ Stabilized APIs
 Cargo
 -----
 - [Cargo API token location moved from `~/.cargo/config` to
-  `~/cargo/credentials`.][cargo/3978]
+  `~/.cargo/credentials`.][cargo/3978]
 - [Cargo will now build `main.rs` binaries that are in sub-directories of
   `src/bin`.][cargo/4214] ie. Having `src/bin/server/main.rs` and
   `src/bin/client/main.rs` generates `target/debug/server` and `target/debug/client`
@@ -172,7 +172,6 @@ Compatibility Notes
 [`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::as_bytes_mut`]: https://doc.rust-lang.org/std/primitive.str.html#method.as_bytes_mut
-[`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
 [`str::get_mut`]: https://doc.rust-lang.org/std/primitive.str.html#method.get_mut