[AsseticBundle] fixed unit tests

Author: fabpot

src/Symfony/Bundle/AsseticBundle/Tests/DependencyInjection/AsseticExtensionTest.php

@@ -43,7 +43,7 @@ protected function setUp()
  $this->markTestSkipped('Assetic is not available.');
  }
 
- if (false === @include 'PHP/CodeSniffer.php') {
+ if (false === @include_once 'PHP/CodeSniffer.php') {
  $this->markTestSkipped('PHP_CodeSniffer is not installed.');
  }