InvalidArgumentException: Unsupported selector (body>strong i)

```php
$html = '<body><strong><i>123</i></strong></body>';
$dom = new HTML5DOMDocument();
$dom->loadHTML($html);
print_r($dom->querySelector('body>strong i'));
```
Throw InvalidArgumentException:
Unsupported selector (body>strong i)
at vendor/ivopetkov/html5-dom-document-php/src/HTML5DOMDocument/Internal/QuerySelectors.php:512

it's always happend on:
`selectorA>selectorB selectorC`