sui-checkbox with attribute required and value=false should be invalid

[sclausen]

Please read https://github.com/edcarroll/ng2-semantic-ui/blob/master/CONTRIBUTING.md and search
existing issues (both open and closed) prior to opening any new issue and ensure you follow the instructions therein.

Bug description:

Vanilla angular checkboxes with required are invalid if unchecked. This doesn't seem to work with sui-checkbox

Link to minimally-working plunker that reproduces the issue:

Sorry, plunkr doesn't seem to work at all, so I opened a repository with a reproduction. I hope that's okay too.
sclausen/ng2-semantic-ui-checkbox-bug

Version of Angular, ng2-semantic-ui, and Semantic UI:

Angular: 7.0.3

ng2-semantic-ui: 0.9.7

Semantic UI: /