How to capture a screenshot with PHPUnit and Selenium2 when the test fails?

I'm using PHPUnit 4.6 and PHPUnit Selenium 1.4.2 with PhantomJS. I want capture a screenshot with the last page when selenium test fails. In PHPUnit Manual there is a example for Selenium 1, but I'm trying use with Selenium 2, because I need use GhostDriver.

WebTestCase.php

class WebTestCase extends PHPUnit_Extensions_Selenium2TestCase
{
    protected $captureScreenshotOnFailure = TRUE;
    protected $screenshotPath = '/../../screenshots';
    protected $screenshotUrl = 'http://localhost:8080/screenshots';

    protected function setUp() {
        $this->setBrowser('phantomjs');
        $this->setBrowserUrl("http://localhost:8080");
        $this->setHost('localhost');
    }
}

Test.php

class Test extends WebTestCase
{

    public function testTitle()
    {
        $this->url('');
        assertEquals($this->title(), "My App");
    }
}

But this not capture a screenshot.

$ vendor/bin/phpunit 
PHPUnit 4.6-ge85198b by Sebastian Bergmann and contributors.

Configuration read from /MyApp/phpunit.xml

F

Time: 231 ms, Memory: 5.50Mb

There was 1 failure:

1) Test::testTitle
Failed asserting that two strings are equal.
--- Expected
+++ Actual
@@ @@
-''
+'My App'

/MyApp/tests/functional/Test.php:7

FAILURES!                            
Tests: 1, Assertions: 1, Failures: 1.