update rust-lang.github.io to rustc-dev-guide.rust-lang.org

Author: chrissimpkins

doc/adding_lints.md

@@ -459,5 +459,5 @@ don't hesitate to ask on Discord, IRC or in the issue/PR.
 [in_external_macro]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc/lint/fn.in_external_macro.html
 [play]: https://play.rust-lang.org
 [author_example]: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=f093b986e80ad62f3b67a1f24f5e66e2
-[rustc-dev-guide]: https://rust-lang.github.io/rustc-dev-guide/
+[rustc-dev-guide]: https://rustc-dev-guide.rust-lang.org/
 [nightly_docs]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc/