fixes #95: use correct method for conversations example

Author: Alex

examples/conversations/create.php

@@ -18,7 +18,7 @@
 $message->type = 'text';
 
 try {
-    $conversation = $messageBird->conversations->create($message);
+    $conversation = $messageBird->conversations->start($message);
 
     var_dump($conversation);
 } catch (\Exception $e) {