gateway/manta: Bump manta dependencies (#5414)

Internally, triton-go, what manta minio is built on, changed it's internal
error handling. This means we no longer need to unwrap specific error types

This doesn't change any manta minio functionality - it just changes how errors are
handled internally and adds a wrapper for a 404 error

vendor/github.com/joyent/triton-go/authentication/rsa_signature.go

@@ -1,3 +1,11 @@
+//
+// Copyright (c) 2018, Joyent, Inc. All rights reserved.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+//
+
 package authentication
 
 import (