Fix object access

Author: swissspidy

src/WP_CLI/CommandWithMeta.php

@@ -112,8 +112,8 @@ public function list_( $args, $assoc_args ) {
 				function ( $a, $b ) use ( $orderby, $order ) {
 					// Sort array.
 					return 'asc' === $order
-					? $a[ $orderby ] <=> $b[ $orderby ]
-					: $b[ $orderby ] <=> $a[ $orderby ];
+					? $a->$orderby <=> $b->$orderby
+					: $b->$orderby <=> $a->$orderby;
 				}
 			);