GridWrapper height is 0.

```
<ColsWrapper>
  <Col initialWidth={100}> a</Col>
  <Col initialWidth={200}> b</Col>
</ColsWrapper>
```
In the above case, GridWrapper height is 0.

There is no problem if you write as follows.
```
<div style={{ height: 100px; }}
  <ColsWrapper>
    <Col initialWidth={100}> a</Col>
    <Col initialWidth={200}> b</Col>
  </ColsWrapper>
</div>
```
