DeprecationWarning: Unhandled promise rejections are deprecated.

Everything is working pretty well but when I refresh on 1 Container out of 5 that are using redux-connect, I get this:

```
(node:27184) DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
```
Then I realize, the documentation is missing catch for loadOnServer method. I think the Readme needs to be updated.

Example:
```
loadOnServer({...renderProps, store}).then(() => {
const components = renderToStaticMarkup(



);
res.status(200);
res.send('\n' +
renderToString(

)
);
})
.catch(err => {
console.log('Caught Error in Server Render: ');
console.log(err);
});
```

Update the README example for loadOnServer to show handling rejected promises. Start by locating the server-rendering example and compare it with the provided code; done means the documented example includes a catch path for the promise rejection.

Written by the indexing model from the issue text.