Fix a nit of copyright date range

Should be 2018 instead of 20018.

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7364)

crypto/poly1305/poly1305_ieee754.c

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-20018 The OpenSSL Project Authors. All Rights Reserved.
+ * Copyright 2016-2018 The OpenSSL Project Authors. All Rights Reserved.
  *
  * Licensed under the OpenSSL license (the "License").  You may not use
  * this file except in compliance with the License.  You can obtain a copy