Fix the signature for CryptoUtils.bytesToBase64.

lib/src/crypto_utils.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library crypto.crypto_utils;
 
 import 'base64.dart';
 
 /**
  * Utility methods for working with message digests.
@@ skipping 19 matching lines @@
    *
    * If [addLineSeparator] is true, the resulting string will  be
    * broken into lines of 76 characters, separated by "\r\n".
    *
    * If [urlSafe] is true, the result is URL and filename safe.
    *
    * Based on [RFC 4648](http://tools.ietf.org/html/rfc4648)
    *
    */
   static String bytesToBase64(List<int> bytes,
-      [bool urlSafe = false, bool addLineSeparator = false]) {
+      {bool urlSafe: false, bool addLineSeparator: false}) {
     return BASE64.encode(bytes,
         urlSafe: urlSafe, addLineSeparator: addLineSeparator);
   }
 
   /**
    * Converts a Base 64 encoded String into list of bytes.
    *
    * Decoder ignores "\r\n" sequences from input.
    *
    * Accepts both URL safe and unsafe Base 64 encoded strings.
    *
    * Throws a FormatException exception if input contains invalid characters.
    *
    * Based on [RFC 4648](http://tools.ietf.org/html/rfc4648)
    */
   static List<int> base64StringToBytes(String input) {
     return BASE64.decode(input);
   }
 }