Fix gpc nameing

[gnuhub]

go: finding module for package google.golang.org/grpc/naming
github.com/yunify/metad/backends/etcdv3 imports
        github.com/coreos/etcd/clientv3 tested by
        github.com/coreos/etcd/clientv3.test imports
        github.com/coreos/etcd/integration imports
        github.com/coreos/etcd/proxy/grpcproxy imports
        google.golang.org/grpc/naming: module google.golang.org/grpc@latest found (v1.37.0), but does not contain package google.golang.org/grpc/naming