Update link to rustc's TyKind

Author: lowr

book/src/types/rust_types.md

@@ -168,7 +168,7 @@ types. The intention is that, at least when transitioning, rustc would
 implement the `Interner` trait and would map from the [`TyKind`][Rustc-TyKind]
 enum to chalk's [`TyKind`] on the fly, when `data()` is invoked.
 
-[Rustc-TyKind]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/enum.TyKind.html
+[Rustc-TyKind]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_type_ir/sty/enum.TyKind.html
 
 | rustc type | chalk variant (and some notes) |
 | ------------- | ------------------ |