guzzle 6.0 call to undefined method GuzzleHttp\Psr7\Response::xml()

I want to check the xml based responses from server, here is an example of the response format.

<response>
    <code>success</code>
</response>

My existing code,

use GuzzleHttp\Client;

$client = new Client();
$response = $client->post('http://ift.tt/1NUF4lf', [
    'form_params' => [
        'transID' => 1234,
        'orderID' => 6789,
        'token' => '0X45FJH79GD3332'
    ]
]);

$xml = $response->xml();

dd($xml);

However, when I make request to the server error occurs like below.

Call to undefined method GuzzleHttp\Psr7\Response::xml()

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