[WIP] Upgrade pandas>=1.0

[lilleswing]

pandas 1.0 was released in January 2020 and removed many deprecated commands. Hopefully the travis tests can show where we are using deprecated API and we can swap them out one at a time.

[lilleswing]

This seems to be passing the non 3.5 tests which are being dropped in #947. Are there known issues with removing back-words capable pandas that need to be dealt with @mfeurer ?

[mfeurer]

Thanks @lilleswing for picking this up.

Your change appears to work well on the master branch, however, we made some changes to pandas handling in the development branch so I'd like to see how this does there.

As for why we haven't updated yet - we're building on openml-python for generating the meta-data, and the latest release there doesn't know about pandas 1.0 yet. But apparently this isn't an issue in the unit tests which is great.

[mfeurer]

As for why we haven't updated yet - we're building on openml-python for generating the meta-data, and the latest release there doesn't know about pandas 1.0 yet. But apparently this isn't an issue in the unit tests which is great.

We have released a new version of the OpenML connector which works with pandas>=1.0, so this can safely be merged. Thanks a lot for your contribution @lilleswing