Add missing tbody

[Purii]

See https://github.com/zurb/inky/pull/59.

Rendering the HTML output inside a react component would throw a warning.

warning.js?8a56:44 Warning: validateDOMNesting(...): <tr> cannot appear as a child of <table>. See StatelessComponent > table > tr. Add a <tbody> to your code to match the DOM tree generated by the browser.