title: "You cannot define a mapping item when in a sequence" when running phpunit in symfony
body: <p>I'm getting the following errors when I try to run phpunit on my symfony project:</p>
  
  <pre><code>$ phpunit -c app
  
  1) [...]\DefaultControllerTest::testIndex
  Symfony\Component\Config\Exception\FileLoaderLoadException: Cannot import resource "/srv/http/typeform/app/config/config.yml" from "/srv/http/typeform/app/config/config_dev.yml".
  
  /srv/http/typeform/vendor/symfony/src/Symfony/Component/Config/Loader/FileLoader.php:89
  [...]
  /srv/http/typeform/vendor/symfony/src/Symfony/Bundle/FrameworkBundle/Test/WebTestCase.php:39
  /srv/http/typeform/src/QuickyForm/PublicBundle/Tests/Controller/DefaultControllerTest.php:11
  
  Caused by
  Symfony\Component\Yaml\Exception\ParseException: You cannot define a mapping item when in a sequence in "\/srv\/http\/typeform\/app\/config\/config.yml"
  
  /usr/share/pear/Symfony/Component/Yaml/Parser.php:116
  [...]
  /srv/http/typeform/app/bootstrap.php.cache:520
  /srv/http/typeform/vendor/symfony/src/Symfony/Bundle/FrameworkBundle/Test/WebTestCase.php:39
  /srv/http/typeform/src/QuickyForm/PublicBundle/Tests/Controller/DefaultControllerTest.php:11
  </code></pre>
  
  <p>It seems that it crash when I call <code>static::createClient();</code></p>
  
  <p>Here's my config_test.yml</p>
  
  <pre><code>imports:
      - { resource: config_dev.yml }
  </code></pre>