title: Elctron clipboard.writeBuffer() doesn't write anything to the clipboard
body: <p>I understand that you can't write multiple custom formats to the clipboard using <code>clipboard.writeBuffer()</code>,
  But when I try to use it write a special format (not text, html, image or rtf), nothing is written to the clipboard:
  <code>const buffer = Buffer.from('slide format data');</code>
  <code>clipboard.writeBuffer(&quot;application/special-format&quot;, buffer);</code>
  and consequently, nothing is being pasted when
  <code>webcontent.paste()</code> is called.</p>
  <p>That being said, I am able to read the buffer from the clipboard using <code>clipboard.readBuffer()</code>,
  but <code>clipboard.availbaleFormtas()</code> returns an empty array.</p>
  <p>Are some formats not supported at all?</p>