use ReactDOM instead of deprecated React.render

Since your blog post, it looks like React has separated out react-dom and deprecated React.render. These are the console errors I get:

```
Warning: React.render is deprecated. Please use ReactDOM.render from require('react-dom') instead.warning @ bundle.js:9378newFn @ bundle.js:26937(anonymous function) @ bundle.js:7414__webpack_require__ @ bundle.js:20(anonymous function) @ bundle.js:48__webpack_require__ @ bundle.js:20(anonymous function) @ bundle.js:40(anonymous function) @ bundle.js:43
bundle.js:9378 Warning: render(): Rendering components directly into document.body is discouraged, since its children are often manipulated by third-party scripts and browser extensions. This may lead to subtle reconciliation issues. Try rendering into a container element created for your app.
```

The fix is just `npm install --save react-dom` and add change app.js to the following:

``` javascript
import React from 'react';
import ReactDOM from 'react-dom';
import Home from './home/home';

ReactDOM.render(, document.body);
```

I can create a PR if you want. That still doesn't fix the warning for rendering to the body, but that's a separate issue.

Start by checking app.js and the project dependency setup, then run the reported app to confirm the React.render warning. Install react-dom and update app.js so rendering uses ReactDOM; done means the deprecated React.render warning is gone, while the document.body warning remains a separate issue.

Written by the indexing model from the issue text.