raft: fix overflow
raft: fix overflow

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