fixed typos in the doc

doc/extensions/http_cache.rst

@@ -24,7 +24,7 @@ Registering
 ::
 
     $app->register(new Silex\Extension\HttpCacheExtension(), array(
-        'cache_dir' => __DIR__.'/cache/',
+        'http_cache.cache_dir' => __DIR__.'/cache/',
     ));
 
 Usage
@@ -42,7 +42,7 @@ setting Response HTTP cache headers::
 This extension allows you to use the Symfony2 reverse proxy natively with
 Silex applications by using the `http_cache` service to handle the Request::
 
-    $app['http_cache']->handle($request)->send();
+    $app['http_cache']->handle()->send();
 
 The extension also provide `ESI
 <http://www.doctrine-project.org/docs/dbal/2.0/en/>`_ support::
@@ -69,7 +69,7 @@ The extension also provide `ESI
         ));
     });
 
-    $app['http_cache']->handle($request)->send();
+    $app['http_cache']->handle()->send();
 
 For more information, consult the `Symfony2 HTTP Cache documentation
 <http://symfony.com/doc/current/book/http_cache.html>`_.