use kafka_err2str (#14)

Author: PyaeSoneAungRgn

Diff for: src/ext-php-simple-kafka-client/pure-php/producer.php

@@ -22,7 +22,7 @@
 // you can see if your message was truly sent, this can be especially of importance if you poll async
 $conf->setDrMsgCb(function (Producer $kafka, Message $message) {
     if (RD_KAFKA_RESP_ERR_NO_ERROR !== $message->err) {
-        $errorStr = rd_kafka_err2str($message->err);
+        $errorStr = kafka_err2str($message->err);
 
         echo sprintf('Message FAILED (%s, %s) to send with payload => %s', $message->err, $errorStr, $message->payload) . PHP_EOL;
     } else {