borderWidth property doesn't accept px values
I'm note sure if this is intentional, but the `borderWidth` property doesn't get rendered if its value is specified in `px`.

This **works**:
```js
const style = {
  borderWidth: 1,
 // ...
};
```

This **doesn't work**:
```js
const style = {
  borderWidth: '1px',
 // ...
};
```