Read in the dotfile mapping as a dictionary.

def load_dotfiles(self):
        """Read in the dotfile mapping as a dictionary."""
        if self.args.map and path.exists(self.args.map):
            dotfiles_path = self.args.map
        else:
            dotfiles_path = self.source

        self.log.debug('Loading dotfile mapping from %s', dotfiles_path)

        return self.parse_mapping(dotfiles_path, source=self.source)