Update header

From Project to Author(s) for the catch-all. This file has my
copyright which is retained through the catch-all statement.

Signed-off-by: Alex Ellis (VMware) <alexellis2@gmail.com>

gateway/types/proxy_client.go

-// Copyright (c) OpenFaaS Project 2018. All rights reserved.
+// Copyright (c) OpenFaaS Author(s) 2018. All rights reserved.
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 package types