fix test error

packages/artplayer/src/player/aspectRatioMix.js

@@ -11,7 +11,8 @@ export default function aspectRatioMix(art) {
         get() {
             return $player.dataset.aspectRatio || 'default';
         },
-        set(ratio = 'default') {
+        set(ratio) {
+            if (!ratio) ratio = 'default';
             if (ratio === 'default') {
                 setStyle($video, 'width', null);
                 setStyle($video, 'height', null);