Blog Directory is not showing the list of blogs

The Blogs Directory plugin is being used on multisite. But the listing page is not showing the list of blogs: http://blogs.fasos.maastrichtuniversity.nl/afterbabel/20162017/student-blogs/

I've tried adding the following line in "wp-config.php" file but didn't help:
define(‘BLOGS_DIRECTORY_SLUG’, ‘student-blogs’);