doc: 2015 will be the Year of the Gopher.

Change-Id: Ic2e34f84596b56715d5f41c9a5250f7c9f8e671b
Reviewed-on: https://go-review.googlesource.com/2087Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>
Reviewed-by: Dave Cheney <dave@cheney.net>

doc/contribute.html

@@ -652,7 +652,7 @@ This rigmarole needs to be done only for your first submission.
 <p>Code that you contribute should use the standard copyright header:</p>
 
 <pre>
-// Copyright 2014 The Go Authors. All rights reserved.
+// Copyright 2015 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>