message: Add model multi-attr update to Mirage types
diff: @@ -30,6 +30,7 @@ interface ModelInstanceShared<T> {
  save(): void;
  update<K extends keyof T>(key: K, val: T[K]): void;
  + update<K extends keyof T>(attrs: { [key: K]: T[K] }): void;
  destroy(): void;
  isNew(): boolean;
  isSaved(): boolean;
  