title: Upgrade to Swift 4. iOS Charts won't build
body: <p>I'm using the Charts library from Github.  The documentation indicates the Pod is updated to support XCode 9 and Swift 4 yet I'm getting errors.</p>
  
  <p>I removed the pod by opening the podfile and removing that line.  I then enter Pod Install into terminal, to remove it.  I then reinstalled to make sure I have the most up to date branch.</p>
  
  <p>The instruction is:</p>
  
  <blockquote>
    <p>Add pod 'Charts' to your Podfile.</p>
  </blockquote>
  
  <p>My error message is:</p>
  
  <blockquote>
    <p>Cannot subsript a value of type [String: AnyObject] with an index of
    type NSAttributedStringKey</p>
  </blockquote>
  
  <p>The error occurs on the second and third line of this function:</p>
  
  <pre><code>var attrs = [String : AnyObject]()
  
  attrs[NSFontAttributeName] = description.font
  attrs[NSForegroundColorAttributeName] = description.textColor
  
  ChartUtils.drawText(
      context: context,
      text: descriptionText,
      point: position!,
      align: description.textAlign,
      attributes: attrs
  )
  </code></pre>