Update RELEASES.md

Author: Mark-Simulacrum

RELEASES.md

@@ -135,8 +135,8 @@ Cargo
   These artifacts are produced by Cargo and rustc during the build process.
   End users usually won't need to interact with them, and the layout inside
   `build-dir` is an implementation detail that may change without notice.
-  ([config doc](https://doc.rust-lang.org/nightly/cargo/reference/config.html#buildbuild-dir))
-  ([build cache doc](https://doc.rust-lang.org/nightly/cargo/reference/build-cache.html))
+  ([config doc](https://doc.rust-lang.org/stable/cargo/reference/config.html#buildbuild-dir))
+  ([build cache doc](https://doc.rust-lang.org/stable/cargo/reference/build-cache.html))
   [#15833](https://github.com/rust-lang/cargo/pull/15833)
   [#15840](https://github.com/rust-lang/cargo/pull/15840)
 - The `--target` flag and the `build.target` configuration can now take literal