title: jsdom not support svg？
body: <p>I download <a href="https://github.com/tmpvar/jsdom" rel="nofollow noreferrer">jsdom@11.0.0</a> to make my react project test easier。
  But I find the jsdom can not create svg element。<br>
  code follows:   </p>
  
  <pre><code>const dc = (new JSDOM(`...`)).window.document;
  var svg = dc.createElementNS("http://www.w3.org/2000/svg", "svg");
  var div = dc.createElement("div");
  var svg2 = dc.createElement("svg");
  console.log("svg:", svg, svg.createSVGPoint);
  console.log("div:", div);
  console.log("svg2:", svg2, svg2.createSVGPoint);
  </code></pre>
  
  <p>and the result is ：</p>
  
  <pre><code>svg: HTMLUnknownElement {} undefined
  div: HTMLDivElement {}
  svg2: HTMLUnknownElement {} undefined
  </code></pre>
  
  <p>I want to do some test in my code, but svg is not work。<br />
  I need help。
  Thank you very much！</p>