devtools/create_migration.sh: change year to 2021

Change-Id: I04a7a8df9bda53e21a7450dadcd2633a16b5f88a
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/282118
Reviewed-by: Jonathan Amsterdam <jba@google.com>
Trust: Julie Qiu <julie@golang.org>
diff --git a/devtools/create_migration.sh b/devtools/create_migration.sh
index bf2e57b..14ec9ef 100755
--- a/devtools/create_migration.sh
+++ b/devtools/create_migration.sh
@@ -7,7 +7,7 @@
 # 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.