Support false value to disable rule in .nrlintrc.js file

[kazuhitoyokoi]

• [x] Bugfix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)

Proposed changes

I forget the background of why true and "off" are used to enable and disable rules in the .nrlintrc.js configuration file. Because I think that true and false are natural for this case, I try to add support for the false value in this pull request.

Checklist

• [x] I have read the contribution guidelines
• [ ] For non-bugfix PRs, I have discussed this change on the forum/slack team.