Second Pull Request - Project Course (ThreadBoard)

Based from my [comment] (https://github.com/fpambid/Board_Exercises/pull/2/files#r17766843) here, you may change L51 ~ 54 to this and remove the method parameters in L44
```php
$row = $db->row('SELECT * FROM user WHERE username = ? AND password = ?', array($this->username, $this->password));
```