Failed to do dynamic loading with redux-router

## Version
2.1.2
## Steps to reproduce
Create a router like below:

```javascript
const rootRouter = {
childRoutes:[{
path:'/root',
component:MainEntry,
childRoutes: [
require('../containers/main_entry')
]
}]
}

return

{rootRouter}

```

but when loading the page, I got below error:

Objects are not valid as a React child (found: object with keys {childRoutes}). If you meant to render a collection of children, use an array instead or wrap the object using createFragment(object) from the React add-ons.

## Expected Behavior

## Actual Behavior