Fix currency test

Author: mindgraffiti

WooCommerce/Classes/Tools/Currency/Currency.swift

@@ -12,7 +12,7 @@ struct Currency {
         case rightSpace = "right_space"
     }
 
-    var amount: NSDecimalNumber
+    var amount: String?
 
     let code: Code
 

WooCommerce/WooCommerceTests/Tools/CurrencyTests.swift

@@ -9,7 +9,7 @@ class CurrencyTests: XCTestCase {
     /// Test currency symbol lookup returns correctly encoded symbol.
     ///
     func testCurrencySymbol() {
-        let currency = Currency(amount: 0.00, code: .AED, position: .left)
+        let currency = Currency(amount: "0.00", code: .AED, position: .left)
         let symbol = currency.symbol
         XCTAssertEqual("د.إ", symbol)
     }