Update http_client.rst

Co-authored-by: Oskar Stark <oskarstark@googlemail.com>

Author: alamirault

http_client.rst

@@ -2037,8 +2037,8 @@ To return json, you would normally do::
     use Symfony\Component\HttpClient\Response\MockResponse;
 
     $response = new MockResponse(json_encode([
-        'foo' => 'bar',
-    ]), [
+            'foo' => 'bar',
+        ]), [
         'response_headers' => [
             'content-type' => 'application/json',
         ],