Fixing line chart with SVG resize tooltip issues.

examples/lineChartSVGResize.html

@@ -23,7 +23,7 @@ svg {
     <a href="#" id="zoomIn">Zoom In</a> <a href="#" id="zoomOut">Zoom Out</a>
   </div>
 
-  <div id="chart1">
+  <div id="chart1" class='with-transitions'>
     <svg></svg>
   </div>
 

src/tooltip.js

@@ -90,6 +90,9 @@ window.nv.tooltip.* also has various helper methods.
         function convertViewBoxRatio() {
             if (chartContainer) {
               var svg = d3.select(chartContainer);
+              if (svg.node().tagName !== "svg") {
+                 svg = svg.select("svg");
+              }
               var viewBox = (svg.node()) ? svg.attr('viewBox') : null;
               if (viewBox) {
                 viewBox = viewBox.split(' ');