Change gae to apache 2 license.

service/mail/interface.go

-// Copyright 2015 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
+// Copyright 2015 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
 
 package mail
 
 // Interface is the interface for all of the mail methods.
 //
 // These replicate the methods found here:
 // https://godoc.org/google.golang.org/appengine/mail
 type Interface interface {
         Send(msg *Message) error
         SendToAdmins(msg *Message) error
 
         Testable() Testable
 }