Backport of MAGETWO-59258: Override module-directory/etc/zip_codes.xml only the last code of a country gets include

Author: simpleadm

app/code/Magento/Directory/Model/Country/Postcode/Config/Reader.php

@@ -12,7 +12,10 @@ class Reader extends \Magento\Framework\Config\Reader\Filesystem
      *
      * @var array
      */
-    protected $_idAttributes = ['/config/zip' => 'countryCode'];
+    protected $_idAttributes = [
+        '/config/zip' => 'countryCode',
+        '/config/zip/codes/code' => 'id',
+    ];
 
     /**
      * Construct the FileSystem Reader Class