`seth events` and `seth logs` send invalid JSON-RPC field

Both `seth events` and `seth logs` use the JSON-RPC command `eth_newFilter`. However, they send an invalid command, `append`. I don't know enough about the JSON-RPC API to tell if this is an old command, or what's wrong, but in any case, this is not working. Setting the SETH_API env var doesn't seem to solve the issue. However, with `seth logs` the issue does go away if you specify a topic.

```
$ seth events 0x35D1b3F3D7966A1DFe207aa4514C12a259A0492B
seth-rpc: {"id":1,"jsonrpc":"2.0","method":"eth_newFilter","params":[{"address":"0x35D1b3F3D7966A1DFe207aa4514C12a259A0492B","append":"","fromBlock":"earliest"}]}
seth-rpc: error: code -32602
seth-rpc: error: message Invalid params: unknown field `append`, expected one of `fromBlock`, `toBlock`, `blockHash`, `address`, `topics`, `limit`.
```