[Spec] Dictionary members should be sequence not FrozenArray (#201)

See whatwg/webidl#900

Author: stephenmcgruer

spec.bs

@@ -541,7 +541,7 @@ Add the following to the [=registry of standardized payment methods=] in
     dictionary SecurePaymentConfirmationRequest {
         required BufferSource challenge;
         required USVString rpId;
-        required FrozenArray<BufferSource> credentialIds;
+        required sequence<BufferSource> credentialIds;
         required PaymentCredentialInstrument instrument;
         unsigned long timeout;
         DOMString payeeName;