message: docs: fix callout header
  PR Close
diff: @@ -73,8 +73,8 @@ the component **subscribes** to the method's return value.
  The subscription callback copies the data fields into the component's `config` object,
  which is data-bound in the component template for display.
  -<div class="alert is-helpful">
  -**Why write a service?**
  +<div class="callout is-helpful">
  + <header>Why write a service?</header>
  This example is so simple that it is tempting to write the `Http.get()` inside the
  component itself and skip the service.
  