minor changes in Query class

small improvements for new documentation in https://github.com/ruflin/Elastica.io/pull/27
You can always do "manual check"

```php
if (!$rescore instanceof AbstractRescore) {
    throw new \LogicException(sprintf('Instance of AbstractRescore expected, but %s was given.', get_type($rescore)));
}

return $this->setParam('rescore', $rescore->toArray());
```

About the release process, it doesn't matter if change like this is in master branch, but it does matter if it's in some release-branch and if it it's tagged.