fix version number

Author: Eh2406

src/libcore/internal_macros.rs

@@ -74,7 +74,7 @@ macro_rules! forward_ref_binop {
 macro_rules! forward_ref_op_assign {
     (impl $imp:ident, $method:ident for $t:ty, $u:ty) => {
         forward_ref_op_assign!(impl $imp, $method for $t, $u,
-                #[stable(feature = "op_assign_builtins_by_ref", since = "1.18.0")]);
+                #[stable(feature = "op_assign_builtins_by_ref", since = "1.22.0")]);
     };
     (impl $imp:ident, $method:ident for $t:ty, $u:ty, #[$attr:meta]) => {
         #[$attr]