use dep as denpendency managment tool

vendor/github.com/docker/distribution/registry/api/v2/doc.go

@@ -1,9 +0,0 @@
-// Package v2 describes routes, urls and the error codes used in the Docker
-// Registry JSON HTTP API V2. In addition to declarations, descriptors are
-// provided for routes and error codes that can be used for implementation and
-// automatically generating documentation.
-//
-// Definitions here are considered to be locked down for the V2 registry api.
-// Any changes must be considered carefully and should not proceed without a
-// change proposal in docker core.
-package v2