Update Connection.php

These changes are imported from :
Fix parsing of NodesInfo for Sniffing
Closes elastic#629 and elastic#648
for sniffing to work properly.

elastic@c0ed43c

src/Elasticsearch/Connections/Connection.php

@@ -445,7 +445,7 @@ public function sniff()
             ]
         ];
 
-        return $this->performRequest('GET', '/_nodes/_all/clear', null, null, $options);
+        return $this->performRequest('GET', '/_nodes/', null, null, $options);
     }
 
     /**