Yes, this broke yesterday due to an updated dependency in core, the PR is already on my to-do-list and will be available later today or tomorrow.
quick fixes:
Option 1 check out Discourse 91c94f which is the commit before the breaking change
Option 2 change gem 'ffi', '1.15.5', require: false in the plugin to gem 'ffi', '1.16.2', require: false