site: update for changes in sapper stores

site/src/components/TopNav.svelte

@@ -1,13 +1,15 @@
 <script>
 	import { onMount } from 'svelte';
 	import Icon from './Icon.svelte';
-	import { page } from '@sapper/app';
+	import { stores } from '@sapper/app';
 
 	export let segment;
 
 	let open = false;
 	let visible = true;
 
+	const { page } = stores();
+
 	// hide nav whenever we navigate
 	page.subscribe(() => {
 		open = false;

site/src/routes/_layout.svelte

@@ -1,10 +1,12 @@
 <script>
-	import { page, preloading } from '@sapper/app';
+	import { stores } from '@sapper/app';
 	import InlineSvg from '../components/InlineSvg.svelte';
 	import PreloadingIndicator from '../components/PreloadingIndicator.svelte';
 	import Nav from '../components/TopNav.svelte';
 
 	export let segment;
+
+	const { preloading, page } = stores();
 </script>
 
 {#if $preloading}