src/Handler.php
protected function sanitizeFileName($name)
    {
        if ($this->sanitizerCallback) {
            return call_user_func($this->sanitizerCallback, $name);
        }
        return preg_replace('/[^A-Za-z0-9\.]+/', '_', $name);
    }
protected function sanitizeFileName($name)
    {
        if ($this->sanitizerCallback) {
            return call_user_func($this->sanitizerCallback, $name);
        }
        return preg_replace('/[^A-Za-z0-9\.]+/', '_', $name);
    }
Sanitize the name of the uploaded file by stripping away bad characters
and replacing "invalid" characters with underscore _

@param  string $name
@return string