title: cannot write mode RGBA as JPEG
body: <p>I am learning to use 'pillow 5.0' following book 'Automate the boring stuff with python'</p>
  
  <p>The info about the image object</p>
  
  <pre><code>In [79]: audacious = auda
  In [80]: print(audacious.format, audacious.size, audacious.mode)
  PNG (1094, 960) RGBA
  </code></pre>
  
  <p>When I tried to convert filetype, it report error.</p>
  
  <pre><code>In [83]: audacious.save('audacious.jpg')
  OSError: cannot write mode RGBA as JPEG
  </code></pre>
  
  <p>There's no such a
  n error in book.</p>