fix invalid target in scans

[FiveOFive]

An extra space is causing an invalid target in every scan result. This fix is to remove the extra space from the args passed to nmap.

Details to reproduce:
Run a scan such as the code below:

const opts = {
  range: ['scanme.nmap.org']
};

nmap.scan(opts, function(err, report) {
  console.log(JSON.stringify(report, null, 2));
});

The output, contains an invalid target entry with empty specification.

"target": [
  {
    "item": {
        "specification": "",
        "status": "skipped",
        "reason": "invalid"
      }
    }
]

And there are two spaces in the args between the ports and the host

"args": "nmap --host-timeout=120s -T4 -oX - -p1-1024  scanme.nmap.org",