clientv3util: fix govet warning
clientv3util: fix govet warning

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

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