Abide - "required" checkboxes do not validate

How to reproduce:

1. Use the latest code from version 6.7.5:
2. Create an "abide-ready" form (data-abide novalidate)
3. Add a checkbox input with the required attribute, a "form-error" span, and a submit button.
4. Load the form and submit without checking the checkbox.

## What should happen?

Prevent submit and display error.

## What happens instead?

Form submits

## Your Environment
I used the latest version via bower available (which is 6.7.5). If I am using an older version the problem doesn't exist.

Reproduce the issue with an abide-ready form containing a required checkbox, form-error span, and submit button, using the version described in the report. Trace the checkbox validation and submit handling; done means an unchecked required checkbox prevents submission and displays the error.

Written by the indexing model from the issue text.