プライベートのプロジェクトで"dep ensure -add github.com/xxx"すると以下のエラーが出た。 Solving failure: No versions of github.com/xxx met constraints: 0.1.1: Could not introduce github.com/xxx@master, as its subpackage github.com/xxx does …

depで"does not contain usable Go code (*build.NoGoError).. (Package is required by (root).)"のエラー