install react-test-render for removing enzyme warning

Enzyme recently made a fix for console warning if we use React v15.5+ , See issue here: enzymejs/enzyme#876

To fix that, we have to install react-test-render instead of react-addons-test-utils

Warning:
``` 
 console.error node_modules/fbjs/lib/warning.js:36
    Warning: ReactTestUtils has been moved to react-dom/test-utils. Update references to remove this warning.

  console.error node_modules/fbjs/lib/warning.js:36
    Warning: Shallow renderer has been moved to react-test-renderer/shallow. Update references to remove this warning.
```

docs/TutorialReact.md

@@ -178,7 +178,7 @@ The code for this example is available at
 
 If you'd like to assert, and manipulate your rendered components you can use [Enzyme](http://airbnb.io/enzyme/) or React's [TestUtils](http://facebook.github.io/react/docs/test-utils.html). We use Enzyme for this example.
 
-You have to run `npm install --save-dev enzyme react-addons-test-utils` to use Enzyme (`react-addons-test-utils` is a peer dependency).
+You have to run `npm install --save-dev enzyme react-addons-test-utils` to use Enzyme (`react-addons-test-utils` is a peer dependency). If your react version is above 15.5+, run `npm install --save-dev enzyme react-test-render` to use Enzyme instead.
 
 Let's implement a simple checkbox which swaps between two labels: