rafthttp: fix from go vet, go lint
rafthttp: fix from go vet, go lint

wantonsolutions/dinv-etcd,StorReduce/etcd,CrazyJvm/etcd,zaphod-concur/etcd,fanminshi/etcd,a-robinson/etcd,swingbach/etcd,rchicoli/etcd,westhood/etcd,gyuho/etcd,mqliang/etcd,mkumatag/etcd,heyitsanthony/etcd,jlamillan/etcd,cockroachdb/etcd,endocode/etcd,bluebreezecf/etcd,akauppi/etcd,insequent/etcd,glycerine/etcd,qqsun8819/etcd,lumjjb/etcd,dannysauer/etcd,dannysauer/etcd,ajityagaty/etcd,westhood/etcd,a-robinson/etcd,rnaveiras/etcd,etcd-io/etcd,plasticbox/etcd,handsomesun/etcd,sinsharat/etcd,etcd-io/etcd,chipironcin/etcd,swingbach/etcd,luxas/etcd,hongchaodeng/etcd,xiang90/etcd,YuleiXiao/etcd,lumjjb/etcd,xiang90/etcd,nekto0n/etcd,wantonsolutions/dinv-etcd,qqsun8819/etcd,mickep76/etcd,lorneli/etcd,YuleiXiao/etcd,jonboulle/etcd,ravigadde/etcd,jlamillan/etcd,vimalk78/etcd,coreos/etcd,ajityagaty/etcd,visheshnp/etcd,rnaveiras/etcd,rchicoli/etcd,OyTao/etcd_learning,glycerine/etcd,purpleidea/etcd,luxas/etcd,li-ang/etcd,rnaveiras/etcd,ktateish/etcd,yudai/etcd,ajityagaty/etcd,glevand/coreos--etcd,linuxcer/etcd,bluebreezecf/etcd,ravigadde/etcd,StorReduce/etcd,lorneli/etcd,visheshnp/etcd,CrazyJvm/etcd,OyTao/etcd_learning,coreos/etcd,hongchaodeng/etcd,sebrandon1/etcd,cockroachdb/etcd,akauppi/etcd,mkumatag/etcd,li-ang/etcd,sofuture/etcd,joshix/etcd,bdarnell/etcd,endocode/etcd,joshix/etcd,zaphod-concur/etcd,armstrongli/etcd,jonboulle/etcd,whuwxl/etcd,tguangch/etcd,chipironcin/etcd,sinsharat/etcd,armstrongli/etcd,gyuho/etcd,heyitsanthony/etcd,whuwxl/etcd,mkumatag/etcd,tguangch/etcd,mickep76/etcd,ktateish/etcd,plasticbox/etcd,linuxcer/etcd,insequent/etcd,nekto0n/etcd,etcd-io/etcd,mqliang/etcd,sebrandon1/etcd,vimalk78/etcd,mqliang/etcd,yudai/etcd,purpleidea/etcd,bdarnell/etcd,handsomesun/etcd,glevand/coreos--etcd,sofuture/etcd,fanminshi/etcd,wantonsolutions/dinv-etcd