React PropTypes deprecation warning
Using the package with React 15.5 triggers this warning:
```
Warning: Accessing PropTypes via the main React package is deprecated. Use the prop-types package from npm instead.
```
More info is here: https://facebook.github.io/react/blog/2017/04/07/react-v15.5.0.html

Note that with React 16.0 it will be removed.