Fix domain per 5f20643

Author: Wilfred

guides/hack/21-XHP/16-extending.md

@@ -387,7 +387,7 @@ use namespace Facebook\XHP\Core as x;
 final xhp class ui_get_status extends x\element {
 
   protected async function renderAsync(): Awaitable<x\node> {
-    $ch = \curl_init('https://status.fb.com/graph-api');
+    $ch = \curl_init('https://metastatus.com/graph-api');
     \curl_setopt($ch, \CURLOPT_USERAGENT, 'hhvm/user-documentation example');
     $status = await \HH\Asio\curl_exec($ch);
     return <x:frag>Status is: {$status}</x:frag>;