Fix deprecation in tree builder

Author: alcaeus

DependencyInjection/Configuration.php

@@ -87,7 +87,14 @@ public function getConfigTreeBuilder()
     {
         $self            = $this;
         $builder         = new TreeBuilder();
-        $node            = $builder->root('doctrine_cache', 'array');
+
+        if (\method_exists($builder, 'getRootNode')) {
+            $node = $builder->getRootNode();
+        } else {
+            // BC layer for symfony/config 4.1 and oler
+            $node = $builder->root('doctrine_cache');
+        }
+
         $normalization   = function ($conf) use ($self, $builder) {
             $conf['type'] = isset($conf['type'])
                 ? $conf['type']