CI: window 37_141 jobs needs to update numpy version

https://github.com/pandas-dev/pandas/blob/master/ci/deps/azure-windows-37.yaml

we no longer support this, I guess it *still* works ok. But we should advance this job to be numpy 1.15* at least, i would say we should actually test numpy 1.18* here.

might also need to actually rename the job to reflect the update.