fix raft_server.go isPeersChanged bug
fix raft_server.go isPeersChanged bug

chrislusf/seaweedfs,hxiaodon/seaweedfs,chrislusf/seaweedfs,chrislusf/seaweedfs,hxiaodon/seaweedfs,chrislusf/seaweedfs,k85169336/seaweedfs,k85169336/seaweedfs