message: test(svg): add `repeat` selector for `svg-backgroundColor` test case.
diff: <script src="./lib/config.js"></script>
  <script src="../dist/zrender.js"></script>
  <meta name="viewport" content="width=device-width, initial-scale=1" />
  + <style>
  + #repeat {
  + position: absolute;
  + top: 10px;
  + left: 10px;
  + }
  + </style>
  </head>
  <body>
  <div id="main" style="width:100vw;height:100vh;"></div>
  + <div class="opt-bar">
  + <button onclick="updateBg()">Change Background</button>
  + <select id="repeat">
  + <option value="">repeat</option>
  + <option value="repeat-x">repeat-x</option>
  + <option value="repeat-y">repeat-y</option>
  + <option value="no-repeat">no-repeat</option>
  + </select>
  + </div>
  <script type="text/javascript">
  var zr = zrender.init(document.getElementById('main'), {
  renderer: 'svg'
  imageDom.src = `https://picsum.photos/seed/picsum/400/200`
  var pattern = {
  image: imageDom,
  - repeat: 'repeat-x'
  + // repeat: 'repeat-x'
  + // repeat: 'repeat-y'
  + // repeat: 'no-repeat'
  };
  + document.querySelector('#repeat').addEventListener('change', e => {
  + if (bg.image) {
  + bg.repeat = e.target.value;
  + zr.setBackgroundColor(bg);
  + }
  + });
  +
  var i = 0;
  + var bg;
  function updateBg() {
  var text;
  - var bg;
  var mod = i % 5;
  if (mod === 0) {
  text = 'pattern';
  updateBg();
  - // setInterval(updateBg, 3e3);
  -
  window.addEventListener('resize', function() {
  zr.resize();
  // zr.setBackgroundColor(pattern);
  