Fix severe regression on HHVM.

Apparently HHVM is more strict than PHP in stream_socket_client() and does not
like at all IPv4 addresses and hostnames eclosed in square brackets. Note that
it is not that weird as square brackets are mandatory only when IPv6 addresses
are embedded in URI strings, so it is more like a weird incompatiblity of HHVM
with the behaviour of the standard PHP interpreter. The connect() attempt fails
but not due to the server being unavailable or some connectivity issue.

The important lesson is: never rely on undocumented behaviours especially when
targeting different runtimes, and do not forget to run the test suite on every
platform right before release like I unfortunately did.

src/Connection/StreamConnection.php

@@ -152,7 +152,12 @@ class StreamConnection extends AbstractConnection
      */
     protected function tcpStreamInitializer(ParametersInterface $parameters)
     {
-        $address = "tcp://[$parameters->host]:$parameters->port";
+        if (!filter_var($parameters->host, FILTER_VALIDATE_IP, FILTER_FLAG_IPV6)) {
+            $address = "tcp://$parameters->host:$parameters->port";
+        } else {
+            $address = "tcp://[$parameters->host]:$parameters->port";
+        }
+
         $flags = STREAM_CLIENT_CONNECT;
 
         if (isset($parameters->async_connect) && $parameters->async_connect) {