With Twig 1.4 release I have problems to change the Concat operator from "~" to "&"

I've used this code

public function getOperators() {
    return array(
        array(),
        array(
            '&' => array('precedence' => 40, 'class' => 'Twig_Node_Expression_Binary_Concat', 'associativity' => \Twig_ExpressionParser::OPERATOR_LEFT)
        ),
    );
}

but it doesn't work ... with 1.3 it works fine