Update Connection.php

[mamsincl]

Fix function signature of performRequest to match declaration in ConnectionInterface

Issue:

Fatal error: 
Declaration of Elasticsearch\Connections\Connection::performRequest($method, $uri, $params = NULL, $body = NULL, $options = Array, ?Elasticsearch\Transport $transport = NULL) 
must be compatible with 
Elasticsearch\Connections\ConnectionInterface::performRequest(string $method, string $uri, ?array $params = Array, $body = NULL, array $options = Array, ?Elasticsearch\Transport $transport = NULL) 
in /mnt/volume-lon1-01/var/www/xxxx/vendor/elasticsearch/elasticsearch/src/Elasticsearch/Connections/Connection.php on line 49

https://github.com/elastic/elasticsearch-php/issues/989 - but for 6.8.x function missing all type hinting

[elasticmachine]

Since this is a community submitted pull request, a Jenkins build has not been kicked off automatically. Can an Elastic organization member please verify the contents of this patch and then kick off a build manually?