Accessing createClass via the main React package is deprecated

### I'm Submitting a ...

```
[x] Bug report
[ ] Feature request
[ ] Support request
```

### Steps to Reproduce

1. Install react-datetime and the latest react.
2. Run the app.
3. Look at the warnings in the console.

### Expected Results

No warnings

### Actual Results

We see a warning that is "Accessing createClass via the main React package is deprecated..."

### Minimal Reproduction of the Problem

### Other Information (e.g. stacktraces, related issues, suggestions how to fix)

This is due to the react-onclickoutside dependency. You'll need to update it to v6 (6.1.1 is the current latest).