If rows contains Objects it will crash due to Invariant Violation: Objects are not valid as a React child

If there're non React objects in the rows (like instance of Date) the JsonTable fill fail to work.
E.g. See https://github.com/facebook/react/issues/5139

meteor.js?hash=ec96c6f…:913 Invariant Violation: Objects are not valid as a React child (found: Fri Apr 01 2016 21:22:14 GMT+0300 (EEST)). If you meant to render a collection of children, use an array instead or wrap the object using createFragment(object) from the React add-ons.