Allow GroupHandler to set a formatter to all nested handlers

src/Monolog/Handler/GroupHandler.php

@@ -11,6 +11,8 @@
 
 namespace Monolog\Handler;
 
+use Monolog\Formatter\FormatterInterface;
+
 /**
  * Forwards records to multiple handlers
  *
@@ -77,4 +79,16 @@ class GroupHandler extends AbstractHandler
             $handler->handleBatch($records);
         }
     }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function setFormatter(FormatterInterface $formatter)
+    {
+        foreach ($this->handlers as $handler) {
+            $handler->setFormatter($formatter);
+        }
+
+        return $this;
+    }
 }