Update pages.md (#520)

The code `this.post = await fetch('https://api.nuxtjs.dev/posts')...` should in fact be `this.posts = await fetch('https://api.nuxtjs.dev/posts')...`

content/en/guides/directory-structure/pages.md

@@ -163,7 +163,7 @@ Every time you need to get asynchronous data you can use fetch. Fetch is called
       }
     },
     async fetch() {
-      this.post = await fetch('https://api.nuxtjs.dev/posts').then(res =>
+      this.posts = await fetch('https://api.nuxtjs.dev/posts').then(res =>
         res.json()
       )
     }