update docs

packages/artplayer/src/player/aspectRatioMix.js

@@ -9,7 +9,7 @@ export default function aspectRatioMix(art) {
 
     def(art, 'aspectRatio', {
         get() {
-            return $player.dataset.aspectRatio || '';
+            return $player.dataset.aspectRatio || 'default';
         },
         set(ratio) {
             if (!ratio) ratio = 'default';

packages/artplayer/src/player/flipMix.js

@@ -9,7 +9,7 @@ export default function flipMix(art) {
 
     def(art, 'flip', {
         get() {
-            return $player.dataset.flip;
+            return $player.dataset.flip || 'normal';
         },
         set(flip) {
             if (!flip) flip = 'normal';

packages/artplayer/src/player/playbackRateMix.js

@@ -9,7 +9,7 @@ export default function playbackRateMix(art) {
 
     def(art, 'playbackRate', {
         get() {
-            return $player.dataset.playbackRate;
+            return $player.dataset.playbackRate || 1.0;
         },
         set(rate) {
             if (rate) {