Update copyright year
Thinko in
Reported-by: "Wang, Shenhao"
Discussion:
* pg_cast.c
* routines to support manipulation of the pg_cast relation
*
- * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
