React 17 compatibility

Getting these warnings after upgrading react-* to the latest:

```
npm WARN unexpected-react@6.0.1 requires a peer of react@^16.9.0 but none is installed. You must install peer dependencies yourself.
npm WARN unexpected-react@6.0.1 requires a peer of react-test-renderer@^16.9.0 but none is installed. You must install peer dependencies yourself.
```