title: migration from v3 to v4 - tooltip not showing in d3
body: <p>I created a scatter plot using <a href="http://bl.ocks.org/nbremer/801c4bb101e86d19a1d0" rel="nofollow noreferrer">this</a> reference. The code worked very well in v3 but after changing it to the v4, tooltip, x-axis and y-axis not showing up.</p>
  
  <p>I created a <a href="https://plnkr.co/edit/rC6zjcOYX3IqN4vqEG0p?p=preview" rel="nofollow noreferrer">Plunker</a>. I would appreciate it if someone can tell me what's wrong with it.</p>
  
  <pre><code>function showTooltip (d, i) {
  
      //Save the chosen circle (so not the voronoi)
      var element = d3.selectAll(".countries."+d.CountryCode);
  
      //Define and show the tooltip
      $(element).popover({
          placement: 'auto top',
          container: '#chart',
          trigger: 'manual',
          html : true,
          content: function() {
              return "&lt;span style='font-size: 12px; text-align: center;'&gt;" + "&lt;span&gt;" + "Speaker: " + "&lt;/span&gt;" + d.Speaker + "\n"
              + "&lt;span&gt;" + "Duration: " + "&lt;/span&gt;" + Math.round(d.Duration) + "\n" +"&lt;/span&gt;"; }
      });
      $(element).popover('show');
  
      //Make chosen circle more visible
      element.style("opacity", 1)
          .style("stroke-width", 6);
  </code></pre>
  
  <p><strong>Update</strong>:</p>
  
  <p><a href="https://plnkr.co/edit/5alwonzCKi1iwubB3d1D?p=preview" rel="nofollow noreferrer">This</a> is the corrected version for this scatter plot in v4 d3. I corrected it with the help of Lary.</p>