Fix async issue in plugin addition

packages/artplayer/src/plugins/index.js

@@ -37,9 +37,9 @@ export default class Plugins {
         }
     }
 
-    add(plugin) {
+    async add(plugin) {
         this.id += 1;
-        const result = plugin.call(this.art, this.art);
+        const result = await plugin.call(this.art, this.art);
         const pluginName = (result && result.name) || plugin.name || `plugin${this.id}`;
         errorHandle(!has(this, pluginName), `Cannot add a plugin that already has the same name: ${pluginName}`);
         def(this, pluginName, {