Correct copyright date for internal header file

The newly added internal async.h header file had last years date in it.
Reviewed-by: NRichard Levitte <levitte@openssl.org>

crypto/include/internal/async.h

@@ -2,7 +2,7 @@
  * Written by Matt Caswell for the OpenSSL project
  */
 /* ====================================================================
- * Copyright (c) 2015 The OpenSSL Project.  All rights reserved.
+ * Copyright (c) 2016 The OpenSSL Project.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions