godoc/static: update copyright year to 2013

The generated static.go file was missing a license header when it was
created in 2013 in CL 12805046. CL 38165 added a license header, using
the current year in the template. This causes the static.go file to go
"out of date" whenever the year changes.

Change the copyright year to be a fixed year when the file was created.
This way, the TestStaticIsUpToDate test will stop breaking every year.

Updates golang/go#36360
Updates golang/go#11811

Change-Id: If1597b0d93b7eacf23b7de103a6d7e3ca049bb4f
Reviewed-on: https://go-review.googlesource.com/c/tools/+/213119
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>

static/gen.go

@@ -11,7 +11,6 @@ import (
 	"fmt"
 	"go/format"
 	"io/ioutil"
-	"time"
 	"unicode"
 )
 
@@ -101,6 +100,6 @@ func appendQuote(out *bytes.Buffer, data []byte) {
 
 const warning = `// Code generated by "makestatic"; DO NOT EDIT.`
 
-var license = fmt.Sprintf(`// Copyright %d The Go Authors. All rights reserved.
+const license = `// Copyright 2013 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.`, time.Now().UTC().Year())
+// license that can be found in the LICENSE file.`