Make the rendering tests pass in IE11

For 2 test cases, the thresholds were also too low for Chrome on OSX.

test_rendering/spec/ol/style/icon.test.js

@@ -68,7 +68,7 @@ describe('ol.rendering.style.Icon', function() {
       map = createMap('webgl');
       createFeatures(function() {
         expectResemble(map, 'spec/ol/style/expected/icon-webgl.png',
-            IMAGE_TOLERANCE, done);
+            2.0, done);
       });
     });
   });