title: Kendo Tooltip is empty
body: <p>dI use a kendo tooltip on cells of a column of a kendo grid but the content of the tooltip is empty.
  When I use the chrome debugger, values are correctly set but there is nothing in my tooltip.</p>
  
  <pre><code>    $("#gri").kendoTooltip({
          filter: "span.tooltip",
          position: "right",
          content: function (e) {
              var tooltipHtml;
              $.ajax({
                  url: ".." + appBaseUrl + "api/Infobulle?id=" + $(e.target[0]).attr("id"),
                  contentType: "application/json",
                  dataType: "json",
                  data: {},
                  type: "GET",
                  async: false
              }).done(function (data) {   // data.Result is a JSON object from the server with details for the row
                  if (!data.HasErrors) {
                      var result = data.Data;
                      tooltipHtml = "Identifiant : " + result.identifiant;
                  } else {
                      tooltipHtml = "Une erreur est survenue";
                  }
                  // set tooltip content here (done callback of the ajax req)
                  e.sender.content.html(tooltipHtml);
              });
          }
  </code></pre>
  
  <p>Any idea ? Why it is empty ?</p>