satisfy IRender protocol in default root component

This seems to be required in newer versions of Om otherwise people will run into

```
Uncaught Error: Assert failed: Invalid Om component fn,  does not return valid instance
(or (satisfies? IRender x) (satisfies? IRenderState x))
```

I couldn't find the appropriate note in Om's `CHANGES.md` so I could be wrong. It seems that most examples are now using `reify` though.