code: function validateRelativePath(pluginDir) {
    return str => {
      try {
        const stat = fs.statSync(path.join(pluginDir, str));
        return stat.isFile();
      } catch (e) {
        return false;
      }
    };
  }
docs: Return validator for `relative-path` format
  
  @param {string} pluginDir
  @return {function(string): boolean}