docs: fix highlight demo

docs/config.js

@@ -159,6 +159,16 @@ function dplayer3 () {
                     console.log(player);
                 }
             }
+        ],
+        highlight: [
+            {
+                time: 20,
+                text: '这是第 20 秒'
+            },
+            {
+                time: 120,
+                text: '这是 2 分钟'
+            }
         ]
     });
 }