Liqpay 1.3 release

### Changes in the Latest LiqPay Release

There are some changes in the latest LiqPay release:

You can check the details here: [LiqPay PHP SDK - GitHub](https://github.com/liqpay/sdk-php/blob/master/LiqPay.php)

```php
protected $_supportedCurrencies = array(
    'EUR', 'USD', 'UAH');
```
We no longer have currency constants available.