title: Format to set active font
body: <p>I can use format to set the current font size and color
    quill.format('size', '18px');
    quill.format('color', 'red');
  but when I try to set the font name eg.
    quill.format('font', 'Cursive');
  it has no effect. The font, in this case 'cursive', exists in the font dropdown in the tool bar (and if you select it, it does become the current font).</p>
  
  <p>How can I use format to set the active font?</p>