Make Currency CaseIterable (#259)

Co-authored-by: Andrew Edwards <[email protected]>

Author: Frizlab

Sources/StripeKit/Shared Models/Currency.swift

@@ -6,7 +6,7 @@
 //
 //
 
-public enum Currency: String, Codable {
+public enum Currency: String, Codable, CaseIterable {
     case usd
     case aed
     case afn