Phalcon\Cli\Dispatcher\Exception: MainTask handler class cannot be loaded

I test Phalcon CLI on homestead, cli.php:

<?php
use Phalcon\Loader;
use Phalcon\CLI\Console as ConsoleApp;
use Phalcon\DI\FactoryDefault\CLI as CliDI;
use Phalcon\Db\Adapter\Pdo\Mysql as DbAdapter;

$loader = new Loader();
$loader->registerNamespaces([
    'Task'    => realpath(__DIR__."/Task/"),
])->registerDirs([
    realpath(__DIR__."/Task/"),
])->register();

$arguments = [];
foreach ($argv as $key => $arg) {
    if ($key == 1) {
        $arguments['task'] = $arg;
    } elseif ($key == 2) {
        $arguments['action'] = $arg;
    } elseif ($key >= 3) {
        $arguments['params'][] = $arg;
    }
}

try {
    $di = new CliDI();

    $di->set("db", function (){
        $connection = new DbAdapter([
            "host"     => "localhost",
            "username" => "homestead",
            "password" => "secret",
            "dbname"   => "phalcon",
            "charset"  => "utf8"
        ]);
        return $connection;
    });

    $console = new ConsoleApp();
    $console->setDI($di);
    $console->handle($arguments);
} catch(Exception $e) {
    $message  = get_class($e).": ".$e->getMessage()."\n";
    $message .= " File=".$e->getFile()."\n";
    $message .= " Line=".$e->getLine()."\n";
    $message .= $e->getTraceAsString();

    echo $message;
}

And the same directory , Task/MainTask.php:

<?php

namespace Task;

use Phalcon\CLI\Task as BaseTask;

class MainTask extends BaseTask
{
    public function mainAction(){
        echo "\nThat is the default task and the default action \n";
    }

    public function testAction(array $params) {
        echo sprintf('hello %s', $params[0]) . PHP_EOL;
        echo sprintf('best regards, %s', $params[1]) . PHP_EOL;
    }
}

When I run this command:

$ php cli.php Main main

But it shows me:

Phalcon\Cli\Dispatcher\Exception: MainTask handler class cannot be loaded

I don't know what's wrong, can you help me?