Fixed TreeBuilder::root() symfony 4.3 deprecation (#21)

* Fixed symfony 4.2 deprecation

The "Symfony\Component\Config\Definition\Builder\TreeBuilder::root()" method called for the "qp_woohoolabs_yin" configuration is deprecated since Symfony 4.3, pass the root name to the constructor instead

* [patch-1] Use BC layer for deprecation in symfony/config

see symfony/maker-bundle#324 and doctrine/DoctrineBundle#853

Remove the BC layer when bump to next major version.

src/DependencyInjection/Configuration.php

@@ -14,8 +14,14 @@ class Configuration implements ConfigurationInterface
      */
     public function getConfigTreeBuilder()
     {
-        $treeBuilder = new TreeBuilder();
-        $rootNode = $treeBuilder->root('qp_woohoolabs_yin');
+        $treeBuilder = new TreeBuilder('qp_woohoolabs_yin');
+
+        if (\method_exists($treeBuilder, 'getRootNode')) {
+            $rootNode = $treeBuilder->getRootNode();
+        } else {
+            // BC layer for symfony/config 4.1 and older
+            $rootNode = $treeBuilder->root('qp_woohoolabs_yin');
+        }
 
         $rootNode
             ->children()