Fix missing method `problem` in `Cask::Audit`.
Fix missing method `problem` in `Cask::Audit`.

claui/brew,nandub/brew,Homebrew/brew,claui/brew,reitermarkus/brew,MikeMcQuaid/brew,konqui/brew,sjackman/homebrew,nandub/brew,EricFromCanada/brew,vitorgalvao/brew,MikeMcQuaid/brew,mahori/brew,MikeMcQuaid/brew,EricFromCanada/brew,konqui/brew,vitorgalvao/brew,claui/brew,claui/brew,Homebrew/brew,reitermarkus/brew,konqui/brew,Homebrew/brew,vitorgalvao/brew,JCount/brew,mahori/brew,JCount/brew,Homebrew/brew,mahori/brew,EricFromCanada/brew,MikeMcQuaid/brew,JCount/brew,sjackman/homebrew,mahori/brew,konqui/brew,reitermarkus/brew,vitorgalvao/brew,nandub/brew,reitermarkus/brew,JCount/brew,nandub/brew,sjackman/homebrew,EricFromCanada/brew,sjackman/homebrew