`ERROR: LoadError: type DataType has no field mutable`

I'm having a similar issue to #18 while saving `PyObject` arrays. I have seen that in that issue they mention than deleting the environment solved it. I would very much like to avoid that, since messing with conda environments is always dangerous.

I'm just doing:
```
JLD.save(joinpath(ODINN.root_dir, "test/data/gdirs.jld"), "gdirs", gdirs)
```

Is this normal? What is the issue here?