docs: remove duplicate css classes in example (#1693)

Author: laygir

packages/docs/guide/advanced/extending-router-link.md

@@ -84,7 +84,7 @@ In practice, you might want to use your `AppLink` component for different parts
 <template>
   <AppLink
     v-bind="$attrs"
-    class="inline-flex items-center px-1 pt-1 border-b-2 border-transparent text-sm font-medium leading-5 text-gray-500 focus:outline-none transition duration-150 ease-in-out hover:text-gray-700 hover:border-gray-300 focus:outline-none focus:text-gray-700 focus:border-gray-300 transition duration-150 ease-in-out"
+    class="inline-flex items-center px-1 pt-1 border-b-2 border-transparent text-sm font-medium leading-5 text-gray-500 hover:text-gray-700 hover:border-gray-300 focus:outline-none focus:text-gray-700 focus:border-gray-300 transition duration-150 ease-in-out"
     active-class="border-indigo-500 text-gray-900 focus:border-indigo-700"
     inactive-class="text-gray-500 hover:text-gray-700 hover:border-gray-300 focus:text-gray-700 focus:border-gray-300"
   >