doc: 2017 is the Year of the Gopher

Change-Id: Iac713ae1f322f893c92b3fc47fe9b5719052f9eb
Reviewed-on: https://go-review.googlesource.com/35240Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: David Symonds <dsymonds@golang.org>
Reviewed-by: Minux Ma <minux@golang.org>

doc/contribute.html

@@ -698,7 +698,7 @@ These files will be periodically updated based on the commit logs.
 <p>Code that you contribute should use the standard copyright header:</p>
 
 <pre>
-// Copyright 2016 The Go Authors. All rights reserved.
+// Copyright 2017 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.
 </pre>