Added supported foreign currencies

- https://doc.gopay.com/cs/#currency

Author: vitkutny

src/Gopay/Entity/BasePayment.php

@@ -43,6 +43,10 @@ abstract class BasePayment extends Object
 	private $allowedCurrency = [
 		Gopay::CURRENCY_CZK,
 		Gopay::CURRENCY_EUR,
+		Gopay::CURRENCY_PLN,
+		Gopay::CURRENCY_HUF,
+		Gopay::CURRENCY_GBP,
+		Gopay::CURRENCY_USD,
 	];
 
 	/**

src/Gopay/Gopay.php

@@ -95,6 +95,18 @@ class Gopay extends Object
 	/** @const Euro */
 	const CURRENCY_EUR = 'EUR';
 
+	/** @const Polish zloty */
+	const CURRENCY_PLN = 'PLN';
+
+	/** @const Hungarian forint */
+	const CURRENCY_HUF = 'HUF';
+
+	/** @const British pound */
+	const CURRENCY_GBP = 'GBP';
+
+	/** @const US dollar */
+	const CURRENCY_USD = 'USD';
+
 	// LANGUAGES ===============================================================
 
 	/** @const Czech */