Documentation/upgrades: highlight "go-grpc-prometheus" change
Documentation/upgrades: highlight "go-grpc-prometheus" change

Signed-off-by: Gyu-Ho Lee <3454051ee3341eb69bdf6fca40899cdad4d86496@gmail.com>

ajityagaty/etcd,heyitsanthony/etcd,sinsharat/etcd,joshix/etcd,li-ang/etcd,mkumatag/etcd,glevand/coreos--etcd,vimalk78/etcd,lorneli/etcd,bluebreezecf/etcd,fanminshi/etcd,gyuho/etcd,dannysauer/etcd,vimalk78/etcd,lorneli/etcd,mkumatag/etcd,bluebreezecf/etcd,gyuho/etcd,xiang90/etcd,li-ang/etcd,dannysauer/etcd,ajityagaty/etcd,mqliang/etcd,xiang90/etcd,sinsharat/etcd,etcd-io/etcd,whuwxl/etcd,mqliang/etcd,glevand/coreos--etcd,rnaveiras/etcd,mkumatag/etcd,rnaveiras/etcd,coreos/etcd,bdarnell/etcd,cockroachdb/etcd,fanminshi/etcd,bdarnell/etcd,ajityagaty/etcd,mqliang/etcd,joshix/etcd,rnaveiras/etcd,sebrandon1/etcd,whuwxl/etcd,sebrandon1/etcd,etcd-io/etcd,heyitsanthony/etcd,etcd-io/etcd,cockroachdb/etcd,coreos/etcd