Hello, error listing products in admin

Hello

This plugins is exactly what I need. But it has a little issue, may be you can help me to correct.
The problem is with the last WP and WOO version, and is in this function:

function filter_products($output)
{
$xml = new SimpleXMLElement(html_entity_decode($output)); (The error is in this line)
if ($xml !== false) {
$wooSticker = $xml->addChild(‘option’, __(‘Fixed Qty’, ‘woofix’));
$wooSticker->addAttribute(‘value’, ‘_woofix’);
if (!empty($_GET[‘product_type’]) && $_GET[‘product_type’] == ‘_woofix’) {
$wooSticker->addAttribute(‘selected’, ‘selected’);
}
$output = $xml->asXML();
}
return $output;
}

The error is in line $xml = new SimpleXMLElement(html_entity_decode($output)) on classes/admin-fixed-quantity-price.php file. May be is just a little adjustment.

I am using:
PHP: 5.3.28
WC: 2.4.10
WP: 4.3.1

Thank you for your help

https://ww.wp.xz.cn/plugins/woocommerce-fixed-quantity/