Vendor new queue-worker version

Introduces 0.4.6 of queue-worker - see upstream repo for changes.

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

gateway/vendor/github.com/nats-io/go-nats/context.go

@@ -1,4 +1,15 @@
-// Copyright 2012-2017 Apcera Inc. All rights reserved.
+// Copyright 2016-2018 The NATS Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
 
 // +build go1.7