title: Downloading file with FileSaver
body: <p>I want to download file from my Rest API with FileSaver. In response headers in Content-Disposition I have filename. How can I read header in angular? 
  When I set my service like this:</p>
  
  <pre><code>getPdf() {
  return this.httpClient.get(this.url, {responseType: 'blob'}); } 
  </code></pre>
  
  <p>I can download file without any problems, but when I want to set additionally {observe: 'response'} to read header in options I have error in my browser.</p>
  
  <pre><code>ERROR TypeError: Failed to execute 'createObjectURL' on 'URL': No function was found that matched the signature provided.
  at saveAs (FileSaver.js:112)
  </code></pre>
  
  <p>My function to save file:</p>
  
  <pre><code>this.packageService.getPdf().subscribe(
    pdf =&gt; {
       saveAs(pdf);
    }
  );
  </code></pre>
  
  <p>I added Access-Control-Expose-Headers on my backend, only when i added {observe} there is an error so i can't find solution for this one.</p>