Take `nightly` out of CI.
Take `nightly` out of CI.

By definition nightly is supposed to break
regularly. Let's not allow that to effect
our master build or PR builds.

Undoing particular change made in #36.

Signed-off-by: Ahmet Alp Balkan <c786c8527fd6be7431bb94ca48b6f76cc06787cc@microsoft.com>

marinehero/aspnet-docker,np83/aspnet-docker,jchannon/aspnet-docker,aspnet/aspnet-docker,glennc/aspnet-docker,PeterJausovec/aspnet-docker,friism/aspnet-docker