Make icon-sprite-webgl example usable with Canvas

examples/icon-sprite-webgl.js

@@ -71,8 +71,14 @@ var vector = new ol.layer.Vector({
   source: vectorSource
 });
 
+// Use the "webgl" renderer by default.
+var renderer = exampleNS.getRendererFromQueryString();
+if (!renderer) {
+  renderer = 'webgl';
+}
+
 var map = new ol.Map({
-  renderer: 'webgl',
+  renderer: renderer,
   layers: [vector],
   target: document.getElementById('map'),
   view: new ol.View({