Fix serial mode on Windows

hi.

When more than one node is registered, run command to only first node. (on windows).

For example.

```php
<?php
// Autoloading for plugin command classes.
if (is_file(__DIR__ . '/vendor/autoload.php')) require_once __DIR__ . '/vendor/autoload.php';

Server::node("192.168.8.203", ["username" => "your"], ["web"]);
Server::node("192.168.8.204", ["username" => "your"], ["web"]);

Task::register('hello', function($task){
    $task->exec(function($process){
        $process->run("uname -n");
    }, ["web"]);
});
```

On Linux.

```console
$ php ../bin/altax hello
[192.168.8.203:20564] Run: uname -n
[192.168.8.204:20565] Run: uname -n
web01.example.com
web02.example.com
```

On Windows.

```console
$ php ../bin/altax hello
[192.168.8.203:7108] Run: uname -n
web01.example.com
```

I tried to fix this problem.
Would you mind review my code?