Change the way objects are normalized to avoid multi-levels of json encoding, fixes #560

tests/Monolog/Formatter/ElasticaFormatterTest.php

@@ -44,7 +44,7 @@ class ElasticaFormatterTest extends \PHPUnit_Framework_TestCase
         $expected = $msg;
         $expected['datetime'] = '1970-01-01T00:00:00.000000+00:00';
         $expected['context'] = array(
-            'class' => '[object] (stdClass: {})',
+            'class' => ['stdClass' => []],
             'foo' => 7,
             0 => 'bar',
         );