Fix http server example in homepage (#1801)

This fixes http server example by updating the import path as well as
using respond() correctly.

website/index.html

@@ -104,12 +104,12 @@ <h2 id="example">Example <a href="#example">#</a></h2>
 
       <p>Or a more complex one:</p>
 
-      <pre><code class="typescript language-typescript">import { serve } from "https://deno.land/x/http/server.ts";
+      <pre><code class="typescript language-typescript">import { serve } from "https://deno.land/x/std/http/server.ts";
 const s = serve("0.0.0.0:8000");
 
 async function main() {
-  for await (const req of s) {
-    req.respond({ body: new TextEncoder().encode("Hello World\n") });
+  for await (const { res } of s) {
+    res.respond({ body: new TextEncoder().encode("Hello World\n") });
   }
 }