devtools/create_migration.sh: change year to 2021
Trust: Julie Qiu
# Script for creating a new migration file.
migrate create -ext sql -dir migrations -seq $1
-HEADER="-- Copyright 2020 The Go Authors. All rights reserved.
+HEADER="-- Copyright 2021 The Go Authors. All rights reserved.
-- Use of this source code is governed by a BSD-style
-- license that can be found in the LICENSE file.
