Removed numpy type aliases depreciated as of numpy 1.20.0

[connorfuhrman]

Package utilizes depreciated numpy aliases: https://numpy.org/doc/stable/release/1.20.0-notes.html. This MR removes them.

[MartinBubel]

Hi @connorfuhrman @connorfuhrman-episci
thanks for fixing this one! In fact we are waiting for this one to be merged at GPy.

I recently joined the team of maintainers and will take care of patching paramz asap.
You PR looks perfectly fine! However, could you please edit it to

• pull into the newly created development branch
• remove the commit that changes the version number. We will take care of this after merging another one or two PRs.

Best regards

Martin