code: function hasRole(rbac, role, cb) {
    if (!this.role) {
      cb(null, false);
      return this;
    }
  
    // check existance of permission
    rbac.hasRole(this.role, role, cb);
    return this;
  }
docs: Check if user has assigned a specific role
  @param  {RBAC}  rbac Instance of RBAC
  @param  {String}  name Name of role
  @return {Boolean}      [description]