message: Update virtuals.md
  `required` spelling
diff: @@ -89,7 +89,7 @@ Example: for only one document
  ```ts
  // I couldn't think of a real use case example
  class Sub {
  - @prop({ requried: true, ref: () => Parent }) // providing the type deferred
  + @prop({ required: true, ref: () => Parent }) // providing the type deferred
  public parent: Ref<Parent>;
  }
  