At the time I am looking at the badge, I see:
Looking at both builds, they appeared to be passed:
I haven’t been able to reproduce this but the badge image urls used in the README don’t match AppVeyor’s documentation so I’ve updated them to what is documented for version 2.1's README.
https://ci.appveyor.com/api/projects/status/gdq095nuitwm86il/branch/develop?svg=true
https://ci.appveyor.com/api/projects/status/gdq095nuitwm86il/branch/master?svg=true