Fix the signature for CryptoUtils.bytesToBase64.

lib/src/crypto_utils.dart

Index: lib/src/crypto_utils.dart
diff --git a/lib/src/crypto_utils.dart b/lib/src/crypto_utils.dart
index 84987160b52a78bfc7b55c98255b96f718b1e752..99613ef2d679d746aeb16c3f90c38b7c01cfd0c9 100644
--- a/lib/src/crypto_utils.dart
+++ b/lib/src/crypto_utils.dart
@@ -37,7 +37,7 @@ abstract class CryptoUtils {
    *
    */
   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);
   }