replace 4xx.html and 5xx.html with _error.html

test/app/routes/5xx.html

@@ -1,6 +0,0 @@
-<svelte:head>
-	<title>Internal server error</title>
-</svelte:head>
-
-<h1>Internal server error</h1>
-<p>{error.message}</p>

test/app/routes/_error.html

@@ -2,5 +2,5 @@
 	<title>{status}</title>
 </svelte:head>
 
-<h1>Not found</h1>
+<h1>{status}</h1>
 <p>{error.message}</p>

test/app/routes/blog/[slug].html

@@ -19,7 +19,7 @@
 				return this.error(500, 'something went wrong');
 			}
 
-			return fetch(`blog/${slug}.json`).then(r => {
+			return fetch(`blog/${slug}.json`).then(async r => {
 				if (r.status === 200) {
 					return r.json().then(post => ({ post }));
 					this.error(r.status, '')