docs: update custom transition example (#2069)

Author: skirtles-code

packages/docs/guide/advanced/transitions.md

@@ -38,7 +38,7 @@ const routes = [
 
 ```vue-html
 <router-view v-slot="{ Component, route }">
-  <!-- Use any custom transition and  to `fade` -->
+  <!-- Use a custom transition or fallback to `fade` -->
   <transition :name="route.meta.transition || 'fade'">
     <component :is="Component" />
   </transition>