Typo in doc (used ArrayCollection instead of Collection)

[nikolay-nikitin]

Hi.

It seems like there is a mistake in mapping documentation ("Multiple object" section). We shouldn't use use Doctrine\Common\Collections\ArrayCollection. Probably it was meant ONGR\ElasticsearchBundle\Collection\Collection.

Using of ArrayCollection leads to error in /vendor/ongr/elasticsearch-bundle/Result/Converter.php:

private function isCollection($property, $value)
    {
        if (!$value instanceof Collection) {
            $got = is_object($value) ? get_class($value) : gettype($value);

            throw new \InvalidArgumentException(
                sprintf('Value of "%s" property must be an instance of Collection, got %s.', $property, $got)
            );
        }
    }