Cannot find package "context" error, even after govendor sync

[mirvpgh]

I'm still having trouble installing stern (on Xubuntu 16.04). I ran govendor sync in the stern directory, and it looked like it ran for several seconds. When I run go install (or go build), I get this error: cmd/cli.go:18:2: cannot find package "context" in any of: /root/go/src/github.com/wercker/stern/vendor/context (vendor tree) /usr/lib/go-1.6/src/context (from $GOROOT) /root/go/src/context (from $GOPATH)

Any suggestions?