Can not build serf after getting the source code

[moooofly]

when building from source, I get

[#18#root@ubuntu-dev /go/src/github.com/hashicorp/serf]$go build ./...
# github.com/hashicorp/serf/serf
serf/merge_delegate.go:40:6: n.State undefined (type *memberlist.Node has no field or method State)
serf/merge_delegate.go:40:16: undefined: memberlist.StateLeft

by

serf/serf/merge_delegate.go

Line 40 in 7faa1b0

if n.State == memberlist.StateLeft {

, find that memberlist.StateLeft can not be referenced, as only stateLeft defined in vendor source by https://github.com/hashicorp/serf/blob/master/vendor/github.com/hashicorp/memberlist/state.go#L22

I think vendor dir should be updated.