changed azure pipelines

[DerThorsten]

• created nightly build
• changed mac build slightly

[DerThorsten]

@ukoethe it seems like vigra is curerntly failing on azure piplines on mac with a segfault

55: Test command: /Users/vsts/agent/2.153.2/work/1/s/build/vigranumpy/test/run_vigranumpytest.sh "."
55: Test timeout computed to be: 10000000
55: /Users/vsts/agent/2.153.2/work/1/s/build/vigranumpy/test/run_vigranumpytest.sh: line 1:  2768 Segmentation fault: 11  /Users/vsts/agent/2.153.2/work/envs/vigra/bin/python -c "import nose; nose.main()" .
55/55 Test #55: vigranumpytest ...................***Failed    0.29 sec

I am pretty sure If you trigger a build on your master will fail with the same errors.
To avoid silent failures I would suggest to have a nightly build. This scheduled nightly build was the actual intend of this PR

[hmeine]

What should be done in order to get this approved? I do not understand where the segfault comes from, but having successful macOS builds again would be nice.