Documentation/upgrades: highlight string "health" field
Documentation/upgrades: highlight string "health" field

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

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