Update src/ty.md

Co-authored-by: Michael Goulet <[email protected]>

Author: chenyukang

src/ty.md

@@ -74,7 +74,7 @@ HIR is built, some basic type inference and type checking is done. During the ty
 figure out what the `ty::Ty` of everything is and we also check if the type of something is
 ambiguous. The `ty::Ty` is then used for type checking while making sure everything has the
 expected type. The [`astconv` module][astconv] is where the code responsible for converting a
-`rustc_hir::Ty` into a `ty::Ty` is located, the main routine used is `ast_ty_to_ty`. This occurs
+`rustc_hir::Ty` into a `ty::Ty` is located. The main routine used is `ast_ty_to_ty`. This occurs
 during the type-checking phase, but also in other parts of the compiler that want to ask
 questions like "what argument types does this function expect?"