Dockerfile: remove "cmd/vendor"

Signed-off-by: Gyuho Lee <gyuhox@gmail.com>

Dockerfile

@@ -1,6 +1,5 @@
 FROM golang
 ADD . /go/src/github.com/coreos/etcd
-ADD cmd/vendor /go/src/github.com/coreos/etcd/vendor
 RUN go install github.com/coreos/etcd
 EXPOSE 2379 2380
 ENTRYPOINT ["etcd"]