Username not accepting "." about confide HOT 1 OPEN

<?php

use Zizaco\Confide\UserValidator;
use Zizaco\Confide\UserValidatorInterface;

class CustomConfideValidator extends UserValidator
{

    public $rules = [
        'create' => [
            'username' => 'string',
            'email'    => 'required|email',
            'password' => 'required|min:4',
        ],
        'update' => [
            'username' => 'string',
            'email'    => 'required|email',
            'password' => 'required|min:4',
        ]
    ];

}