Saving h5 files on different hardware sometimes produces issues

[ejolly]

Looks like this might linked to a pytables issue: pandas-dev/pandas#24839

[ejolly]

We should include a minimum pytables version in our requirements which seems to fix this
pytables>=3.5.1

[ejolly]

But that's assuming we have numpy>=1.16. This might require more testing with different combinations of numpy and pytables...