doc: reference does not exist, probably a typo

Author: tshepang

src/librustc_ast/ast.rs

@@ -16,7 +16,7 @@
 //! - [`Lit`] and [`LitKind`]: Literal expressions.
 //! - [`MacroDef`], [`MacStmtStyle`], [`MacCall`], [`MacDelimeter`]: Macro definition and invocation.
 //! - [`Attribute`]: Metadata associated with item.
-//! - [`UnOp`], [`UnOpKind`], [`BinOp`], [`BinOpKind`]: Unary and binary operators.
+//! - [`UnOp`], [`BinOp`], and [`BinOpKind`]: Unary and binary operators.
 
 pub use crate::util::parser::ExprPrecedence;
 pub use GenericArgs::*;