title: Swift 3 UITableView datasource method viewForHeaderInSection gives warning
body: <p>After migration to Swift 3 I have the following method:</p>
  
  <pre><code>func tableView(_ tableView: UITableView, viewForHeaderInSection section: Int) -&gt; UIView? {}
  </code></pre>
  
  <p>And it gives me the warning </p>
  
  <blockquote>
    <p>Instance method 'tableView(tableView:viewForHeaderInSection:)' nearly
    matches optional requirement 'tableView(_:titleForHeaderInSection:)'
    of protocol 'UITableViewDataSource'</p>
  </blockquote>
  
  <p>Fix-it offers to make the method private or add @"nonobjc" annotation. How to resolve the warning? </p>