Make HTTP/403 say "Yikes!"

Summary: This text is significantly more clear and helpful for users.

Test Plan: Tried to do something I'm not suppposed to, hit the 403 page.

Differential Revision: https://secure.phabricator.com/D20847

src/aphront/response/Aphront403Response.php

@@ -28,7 +28,7 @@ final class Aphront403Response extends AphrontHTMLResponse {
     $dialog = id(new AphrontDialogView())
       ->setUser($user)
       ->setTitle(pht('403 Forbidden'))
-      ->addCancelButton('/', pht('Peace Out'))
+      ->addCancelButton('/', pht('Yikes!'))
       ->appendParagraph($forbidden_text);
 
     $view = id(new PhabricatorStandardPageView())