Getting `ValueError: Unable to convert to cesiumpy entity` for loading a shapefile

Was trying to use:

```
res = cesiumpy.io.read_shape("pipelines.shp")
v = cseiumpy.Viewer()
v.entities.add(res, material="red")
v
```

And it gave me that ValueError exception. The pipeline shape file can be downloaded here: https://data.gov.au/dataset/oil-and-gas-pipelines-of-australia

I'm running Python 2 with latest master `cesiumpy==0.4.0.dev0` and `Shapely==1.5.17`.
