docs($plugin-pwa): fixed example for the custom component (#1977)

Author: xr0master

packages/docs/docs/plugin/official/plugin-pwa.md

@@ -214,9 +214,9 @@ First, you need to create a global component (e.g. `MySWUpdatePopup`) at `.vuepr
 
 ```vue
 <template>
-  <SWUpdatePopup>
+  <SWUpdatePopup v-slot="{ enabled, reload, message, buttonText }">
     <div
-      v-slot="{ enabled, reload, message, buttonText }"
+      v-if="enabled"
       class="my-sw-update-popup">
       {{ message }}<br>
       <button @click="reload">{{ buttonText }}</button>

packages/docs/docs/zh/plugin/official/plugin-pwa.md

@@ -214,9 +214,9 @@ module.exports = {
 
 ```vue
 <template>
-  <SWUpdatePopup>
+  <SWUpdatePopup v-slot="{ enabled, reload, message, buttonText }">
     <div
-      v-slot="{ enabled, reload, message, buttonText }"
+      v-if="enabled"
       class="my-sw-update-popup">
       {{ message }}<br>
       <button @click="reload">{{ buttonText }}</button>