add call to fixXmlConfig() such that the channel option can be configured in XML format

Author: xabbuh

DependencyInjection/Configuration.php

@@ -185,6 +185,7 @@ public function getConfigTreeBuilder()
         $rootNode = $treeBuilder->root('monolog');
 
         $rootNode
+            ->fixXmlConfig('channel')
             ->fixXmlConfig('handler')
             ->children()
                 ->arrayNode('channels')