RPC: getconnectioncount error

```
curl -d '{"jsonrpc":"2.0","id":"1","method":"getconnectioncount","params":[]}' http://127.0.0.1:20332
{"jsonrpc":"2.0","id":"1","error":{"code":-32601,"message":"Method not found","data":"   at AntShares.Network.RPC.RpcServer.InternalCall(String method, JArray _params)\n   at AntShares.Network.RPC.RpcServer.ProcessRequest(JObject request)"}}
```
