Fix Windows builds

[Tobias-Fischer]

Issue:
After Ruby has been removed from the Windows CI (see conda-forge/conda-forge-ci-setup-feedstock#103 (comment)), the Windows builds fail (see #8). A conda Ruby build does not seem to be appearing any time soon (conda-forge/ruby-feedstock#30).

Options:

• No Windows builds for a while
• Pushing [WIP] blind attempt to build on windows ruby-feedstock#30 forward
• Putting the Azure Ruby back in the path (ideally separately from the other pre-installed stuff which might interfere)

[Tobias-Fischer]

I think we can simply re-add the Ruby exe to the path, as specified here: https://docs.microsoft.com/en-us/azure/devops/pipelines/ecosystems/ruby?view=azure-devops#use-a-specific-ruby-version

The versions available are listed here: https://github.com/actions/virtual-environments/blob/master/images/win/Windows2016-Readme.md

[wolfv]

but we would have to do this in the conda-forge-ci-setup ideally, right?

[Tobias-Fischer]

Ideally yes .. however we could add the build step just in this repo to start with, although it would be a hack.