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/Gopkg.toml

@@ -25,14 +25,6 @@
   branch = "master"
   name = "github.com/abdullin/seq"
 
-[[constraint]]
-  name = "github.com/davecgh/go-spew"
-  version = "1.1.0"
-
-[[constraint]]
-  branch = "master"
-  name = "github.com/hashicorp/errwrap"
-
 [[constraint]]
   branch = "master"
   name = "github.com/sean-/seed"
@@ -40,3 +32,7 @@
 [[constraint]]
   branch = "master"
   name = "golang.org/x/crypto"
+
+[[constraint]]
+  branch = "master"
+  name = "github.com/pkg/errors"