fix function log from Slim/Log.php

Now you can print mixed variables: $app->log->debug(mixed )

$response = array(  "data" => "value" );
$app->log->debug($response);

and also:

$my_obj = new stdClass;
$my_obj->fix = 1;
$my_obj->email = "contact@alexandrubagu.info";
$app->log->debug($my_obj);