message: test(svg): tweak `svg-backgroundColor` test case
diff: <script src="../dist/zrender.js"></script>
  <meta name="viewport" content="width=device-width, initial-scale=1" />
  <style>
  - #repeat {
  + .opt-bar {
  position: absolute;
  top: 10px;
  left: 10px;
  // repeat: 'no-repeat'
  };
  - document.querySelector('#repeat').addEventListener('change', e => {
  + const repeatSelector = document.querySelector('#repeat');
  + repeatSelector.addEventListener('change', e => {
  if (bg.image) {
  bg.repeat = e.target.value;
  zr.setBackgroundColor(bg);
  function updateBg() {
  var text;
  var mod = i % 5;
  + repeatSelector.style.display = 'none';
  if (mod === 0) {
  text = 'pattern';
  bg = pattern;
  + repeatSelector.style.display = '';
  }
  else if (mod === 1) {
  text = 'radial gradient';
  