The module masonry 8.x requires Masonry jQuery plugin. How can you install it under Drupal 8?
At first, at your drupal 8 root directory create a new folder called "libraries". In directory libraries, create 2 folders respectively: imagesloaded and masonry. You can download the js libraries from both http://masonry.desandro.com/v2/ and http://imagesloaded.desandro.com/.
After downloading the right version js, name them imagesloaded.pkgd.min.js and masonry.pdgd.min.js.
At last, reflesh status report and you will see the warning message has gone.