title: Firebase storage API triggers twice
body: <p>I am trying to store my file using Google Firebase storage API but the pipe is getting executed twice. Any ideas to make it triggered one time only?</p>
  
  <pre class="lang-js prettyprint-override"><code>// def
  task: AngularFireUploadTask;
  storage: AngularFireStorage;
  
  // code
  this.task = this.storage.upload(path, file, { customMetadata });
      return this.task.snapshotChanges().pipe(
          map(doc =&gt; {
              console.log('me'); // THIS IS PRINTED TWICE
              return doc;
          })
      );
  </code></pre>