FrontMatter v1.0.1 invokes YAML.safe_load with arguments that are incompatible with Ruby 2.5, causing an ArgumentError: unknown keyword: permitted_classes. Relevant change at https://github.com/waiting-for-dev/front_matter_parser/pull/11
This is causing CI to break, as the lockfiles in the gemfiles/ dir (used by Appraisal) are not checked into the repo.