Update src/appendix/code-index.md

Fix display string

Co-authored-by: Tshepang Mbambo <[email protected]>

Author: emmet-horgan

src/doc/rustc-dev-guide/src/appendix/code-index.md

@@ -13,7 +13,7 @@ Item            |  Kind    | Short description           | Chapter            |
 `DefId` | struct | One of four types of HIR node identifiers | [Identifiers in the HIR] | [compiler/rustc_hir/src/def_id.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/def_id/struct.DefId.html)
 `Diag` | struct | A struct for a compiler diagnostic, such as an error or lint | [Emitting Diagnostics] | [compiler/rustc_errors/src/diagnostic.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/struct.Diag.html)
 `DocContext` | struct | A state container used by rustdoc when crawling through a crate to gather its documentation | [Rustdoc] | [src/librustdoc/core.rs](https://github.com/rust-lang/rust/blob/master/src/librustdoc/core.rs)
-`HirId` | struct | One of four types of HIR node identifiers | [Identifiers in the HIR] | [compiler/rustc_hir/src/hir_id.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/struct.HirId.html)
+`HirId` | struct | One of four types of HIR node identifiers | [Identifiers in the HIR] | [compiler/rustc_hir_id/src/lib.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/struct.HirId.html)
 `Lexer` | struct | This is the lexer used during parsing. It consumes characters from the raw source code being compiled and produces a series of tokens for use by the rest of the parser | [The parser] |  [compiler/rustc_parse/src/lexer/mod.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/lexer/struct.Lexer.html)
 `NodeId` | struct | One of four types of HIR node identifiers. Being phased out | [Identifiers in the HIR] | [compiler/rustc_ast/src/ast.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_ast/node_id/struct.NodeId.html)
 `P` | struct | An owned immutable smart pointer. By contrast, `&T` is not owned, and `Box<T>` is not immutable. | None | [compiler/rustc_ast/src/ptr.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_ast/ptr/struct.P.html)