migrate to go-modules

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

vendor/github.com/fsouza/go-dockerclient/registry_auth.go

@@ -0,0 +1,10 @@
+// Copyright 2013 go-dockerclient 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 docker
+
+type registryAuth interface {
+	isEmpty() bool
+	headerKey() string
+}