Add 'BuildRequires: golang(github.com/spf13/viper)'
    
    Earlier Viper was being pulled in by Cobra, and hence wasn't explicitly
    listed as a BuildRequires.  However, Cobra 1.4.0 removed the Viper
    dependency [1], so it needs to be explicitly listed.
    
    There's no need to do a build just for this.
    
    [1] Cobra commit 5b2b9e9f61d36ccb
        https://github.com/spf13/cobra/issues/1597