readme: reenable build badge for travis ci

Author: zebastian

README.md

@@ -1,20 +1,23 @@
 PHP bindings for 0MQ. The documentation is available at http://php.net/zmq
 
-The API is roughly as follows:
+[![Build Status](https://travis-ci.org/zeromq/php-zmq.png?branch=master)](https://travis-ci.org/zeromq/php-zmq)
 
-    <?php
+The API is roughly as follows:
 
-    /* Create new queue object */
-    $queue = new ZMQSocket(new ZMQContext(), ZMQ::SOCKET_REQ, "MySock1");
+```php
+<?php
 
-    /* Connect to an endpoint */
-    $queue->connect("tcp://127.0.0.1:5555");
+/* Create new queue object */
+$queue = new ZMQSocket(new ZMQContext(), ZMQ::SOCKET_REQ, "MySock1");
 
-    /* send and receive */
-    var_dump($queue->send("hello there, using socket 1")->recv());
+/* Connect to an endpoint */
+$queue->connect("tcp://127.0.0.1:5555");
 
-    ?>
+/* send and receive */
+var_dump($queue->send("hello there, using socket 1")->recv());
 
+?>
+```
 
 For installation instructions see http://pecl.php.net/zmq