Update package to replace deprecated React.createClass

[mullojo]

React.createClass was deprecated in React 15.5 and needs to be updated per the Migration Guide:

https://reactjs.org/blog/2017/04/07/react-v15.5.0.html#migrating-from-reactcreateclass

We need the following update, without it, this package can't be used past React 15.4. I'm a member of the Meteor community working with others to update @SachaG's Discover Meteor Book that relies on this package. We've almost got the work done, but it would be great to get a hand on this package. We could probably fork it and upload it under a different name, but it would be great to get this fix in place!

// Before (15.4 and below)
import React from 'react';

MeteorGriddle = React.createClass({
});


// After (15.5)
import React from 'react';
var createReactClass = require('create-react-class');

MeteorGriddle = createReactClass({
});