Can’t set ShapePath to type `Custom`
```
let sketch = require('sketch’)
let ShapePath = sketch.ShapePath
const test = new ShapePath({
  shapeType: ShapePath.ShapeType.Custom
})
console.log(test.shapeType)
// returns 'Rectangle’ not 'Custom'
```

Moreover, the documentation is incorrect https://developer.sketch.com/reference/api/#create-a-new-shapepath

```
const shapePath = new ShapePath({
  name: 'my shape path',
  shapePath: ShapePath.ShapeType.Oval,
})

// should be

const shapePath = new ShapePath({
  name: 'my shape path',
  shapeType: ShapePath.ShapeType.Oval,
})
```

Updated the documentation in #467 

---

#### More info on ShapePath
Looks like if a ShapeType is set to `Custom` then it gets defaulted to `Rectangle`. This isn’t good if you want to try and make a Line object.

```
const ShapeTypeMapReverse = {
  Rectangle: MSRectangleShape,
  Oval: MSOvalShape,
  Polygon: MSPolygonShape,
  Star: MSStarShape,
  Triangle: MSTriangleShape,
  Custom: MSRectangleShape, // we are just going to default to Rectangle here
}
```

However, even if you were able to change this and get the ShapeType to custom `Custom` it still doesn’t quite behave like a line that you draw with the line tool. Here is an example where I try to do that:

```
let shapePathLayer = MSShapePathLayer.alloc().init()
let myLine = sketch.fromNative(shapePathLayer)
console.log(myLine.shapeType)
// 'Custom'
myLine.name = 'myLine'
myLine.frame = new Rectangle(0,0,40,100)
myLine.style = { borders: ['#FF0000'] }
myLine.points = [{ point: { x: 0, y: 0 }},{ point: { x: 1, y: 1 }}]
myLine.parent = myArtboard
```

Currently, the workaround that I have with creating a line is this:

```
var path = NSBezierPath.bezierPath()
path.moveToPoint(NSMakePoint(10,10))
path.lineToPoint(NSMakePoint(400,200))
var nativeLine = MSShapeGroup.layerWithPath(MSPath.pathWithBezierPath(path))

let lineShape = sketch.fromNative(nativeLine)
let line = lineShape.layers[0]
line.parent = myArtboard
line.style = { borders: ['#FF0000'] }
```