Volume meshes from surface meshes using pygalmesh crashes

Hi,
could you please update the Volume meshes from surface meshes example section.
Running the example crashes with:
```
pygalmesh volume-from-surface elephant.vtu out.vtk --cell-size 1.0 --odt
usage: pygalmesh [-h] [--version] {from-inr,remesh-surface,volume-from-surface} ...
pygalmesh: error: unrecognized arguments: --cell-size 1.0

```

Best