x/tools/dashboard/app: ignore freebsd-arm failures
x/tools/dashboard/app: ignore freebsd-arm failures

The previous instance of this change was applied to the release branch.
I don't know why the codereview plugin allowed me to do this.
Thankfully we won't be using it for much longer.

TBR=dfc
R=dave
CC=golang-codereviews
https://golang.org/cl/175870044

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