demo fix

docs/lab/index.html

@@ -41,6 +41,7 @@
     <script src="./plugins/codemirror.js"></script>
     <script src="./plugins/javascript.js"></script>
     <script src="./js/artplayer.js"></script>
+    <script src="./js/artplayer-plugin-subtitle.js"></script>
     <script src="./js/common.js"></script>
     <script>
         var _hmt = _hmt || [];