update docs

packages/artplayer/src/player/currentTimeMix.js

@@ -1,8 +1,5 @@
 export default function currentTimeMix(art, player) {
   Object.defineProperty(player, 'currentTime', {
-    get: () => art.refs.$video.currentTime || 0,
-    set: currentTime => {
-      art.refs.$video.currentTime = currentTime;
-    }
+    get: () => art.refs.$video.currentTime || 0
   });
 }