Wiki Plugin causes fatal error

Hi,

after uploading and activating the wiki plugin my wordpress site disappears and I get the following error message:
Fatal error: Call to undefined method WP_Query::is_main_query() in /my/hosting/rp-hosting/client#/project/wp-projekte/taxifisch/wordpress/wp-content/plugins/wiki/wiki-include.php on line 211
What can I do about it?
Thanks for your help,

Elisabeth