Azure not uploading to codecov

[takluyver]

Not high priority yet, but if we're going to drop some jobs on Travis & Appveyor in favour of Azure, we should make sure it's uploading coverage information properly. Currently it gives:

Error: Missing repository upload token

The token itself probably can't be secret if we want it to work for pull requests, but that shouldn't be a big problem:
https://community.codecov.io/t/security-issues-regarding-upload-token/429/6

[tacaswell]

It looks like codecov added support for this 3 days ago: https://blog.codecov.io/2019/01/24/new-in-codecov-4-4-3/ (at least for linux)

[takluyver]

I think I've got this working for the Linux builds in #1356. The Windows & Mac builds say Error: No coverage report found.