chore: bump version to 3.1.3

Author: Alexandru Bucur

src/MessageBird/Client.php

@@ -20,7 +20,7 @@ class Client
     public const ENABLE_CONVERSATIONSAPI_WHATSAPP_SANDBOX = 'ENABLE_CONVERSATIONSAPI_WHATSAPP_SANDBOX';
     public const CONVERSATIONSAPI_WHATSAPP_SANDBOX_ENDPOINT = 'https://whatsapp-sandbox.messagebird.com/v1';
 
-    const CLIENT_VERSION = '3.1.2';
+    const CLIENT_VERSION = '3.1.3';
 
     /**
      * @var Resources\Messages