/**
* Sets the value of the current field to the current date, either as a date or a timestamp.
*
* @see Expr::currentDate()
* @see http://docs.mongodb.org/manual/reference/operator/currentDate/
* @param string $type
* @return self
*/
public function currentDate($type = 'date')
{
$this->expr->currentDate($type);
return $this;
}