Mark class as final

Sources/CryptoSwift/Poly1305.swift

@@ -14,7 +14,7 @@ final public class Poly1305 {
     let blockSize = 16
     private var ctx:Context?
     
-    private class Context {
+    private final class Context {
         var r            = Array<UInt8>(repeating: 0, count: 17)
         var h            = Array<UInt8>(repeating: 0, count: 17)
         var pad          = Array<UInt8>(repeating: 0, count: 17)

Sources/CryptoSwift/SecureBytes.swift

@@ -15,7 +15,7 @@
     import Darwin
 #endif
 
-class SecureBytes {
+final class SecureBytes {
     private let bytes: Array<UInt8>
     let count: Int