wrong socks5h handling



```
    let lookup = false;
    switch (this.proxy.protocol) {
      case 'socks4:':
      case 'socks5h:':      // this line is wrong,  should be 'socks5:' instead
        lookup = true;
        break;
    }
```

See https://github.com/urllib3/urllib3/issues/1035,
Quote: In a proxy string, socks5h:// and socks4a:// mean that the hostname is
resolved by the SOCKS server, not the client
