cloud/storage/b2cs: add missing copyright header

Change-Id: Ie3d4dc9631fa86b94e991da56ef08abb48c10fab
Reviewed-on: https://upspin-review.googlesource.com/16621
Reviewed-by: Rob Pike <r@golang.org>
diff --git a/cloud/storage/b2cs/b2cs_test.go b/cloud/storage/b2cs/b2cs_test.go
index 6e7b75e..67a60a8 100644
--- a/cloud/storage/b2cs/b2cs_test.go
+++ b/cloud/storage/b2cs/b2cs_test.go
@@ -1,3 +1,7 @@
+// Copyright 2017 The Upspin Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
 package b2cs
 
 import (