go.tools/dashboard/builder: fix build
go.tools/dashboard/builder: fix build

TBR=bradfitz
R=bradfitz
CC=golang-codereviews
https://golang.org/cl/151370044

nicot/tools,springning/tools,argandas/tools,4ad/tools,golang/tools,josharian/tools,syreclabs/go-tools,golang/tools,maddyonline/tools,sshetty10/tools,matryer/tools,cw2018/tools,syreclabs/go-tools,matryer/tools,cw2018/tools,nicot/tools,glasser/golang-tools,jdhenke/tools,runcom/tools,glasser/golang-tools,argandas/tools,dmitris/tools,dmitris/tools,cmars/tools,syreclabs/go-tools,dmitris/tools,nicot/tools,jdhenke/tools,springning/tools,dmitris/tools,josharian/tools,magiccao/tools,runcom/tools,golang/tools,cmars/tools,matryer/tools,jdhenke/tools,golang/tools,argandas/tools,josharian/tools,syreclabs/go-tools,argandas/tools,cmars/tools,maddyonline/tools,maddyonline/tools,cw2018/tools,4ad/tools,syreclabs/go-tools,cmars/tools,jdhenke/tools,sshetty10/tools,runcom/tools,magiccao/tools,springning/tools,josharian/tools,springning/tools,maddyonline/tools,4ad/tools,magiccao/tools,syreclabs/go-tools,magiccao/tools,nicot/tools,glasser/golang-tools,cw2018/tools,sshetty10/tools,matryer/tools,runcom/tools,glasser/golang-tools,golang/tools,sshetty10/tools