numpy.product() depreciated

[harzer99]

I am using h5pyd version 0.18.0, which does not seem to enforce a numpy 1.xx version. (I saw there was a past issue discussing this).

It will crash because numpy.product() is depreciated. Afaik it got changed to numpy.prod()

Manually downgrading to a nympy 1.xx version is my current workaround.