I guess we need more builders.

Change-Id: I309e3df7608b9eef9339196fdc50dedf5f9422e4
Reviewed-on: https://go-review.googlesource.com/8434Reviewed-by: Michael Hudson-Doyle <michael.hudson@canonical.com>
Reviewed-by: David Crawshaw <crawshaw@golang.org>
Reviewed-by: Minux Ma <minux@golang.org>