Setting corner radius of ShapePath doesn't work
When setting the corner radius for all the points of a ShapePath the new value is not applied for cornerRadius value under 3.

Steps to reproduce:

1. Create a Rectangle
2. Select it
3. Execute sample code
Sample code:
```
var sketch = require('sketch/dom');
var selectedLayer = sketch.fromNative(context.selection[0]);
var radius = 1;

if (selectedLayer.points && selectedLayer.points.length) {
    selectedLayer.points.forEach(p => p.cornerRadius = radius);
}
```

After executing the sample code the Rectangle has Radius of 3 not 1.

NOTE:

The above example works correctly when replacing this line
`selectedLayer.points.forEach(p => p. cornerRadius = radius);`
with
`selectedLayer.points.forEach(p => p.sketchObject.setCornerRadius(radius));`