Fix typo in labels prop of radio and checkbox.

[aswinshenoy]

Additional description

Fixes typo in labels prop of radio and checkbox component, that have crept in with merging of #1786.

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• TravisCI tests pass. This includes linting, Mocha, Jest, Storyshots, and components/component-docs.json tests.
• Tests have been added for new props to prevent regressions in the future. See readme.
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[kevinparkerson]

Waiting for Travis to pass then it should be good