title: running queries in firebase using async / await
body: <p>Appreciating that firebase has <a href="https://firebase.googleblog.com/2016/01/keeping-our-promises-and-callbacks_76.html" rel="noreferrer">added support for promises</a>, is there a way to run a query like the following inside of an <code>async</code> function?:</p>
  
  <pre><code>const eventref = this.db.ref('cats/whiskers');
  const value = await eventref.once('value')
  </code></pre>
  
  <p>Running the above returns a promise for <code>value</code>, I'm hoping to get the json blob that is stored at <code>cats/whiskers</code>.</p>