added missing file headers

Author: irakliyk

air/src/air/aux.rs

@@ -1,3 +1,8 @@
+// Copyright (c) Facebook, Inc. and its affiliates.
+//
+// This source code is licensed under the MIT license found in the
+// LICENSE file in the root directory of this source tree.
+
 use alloc::{string::ToString, vec::Vec};
 
 use crypto::{ElementHasher, RandomCoin, RandomCoinError};