fix: resource example (#896)

Author: atk

src/routes/guides/fetching-data.mdx

@@ -57,7 +57,7 @@ function App() {
       </Show>
       <Switch>
         <Match when={user.error}>
-          <span>Error: {user.error()}</span>
+          <span>Error: {user.error}</span>
         </Match>
         <Match when={user()}>
           <div>{JSON.stringify(user())}</div>