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/layer/vectortile.test.js

@@ -66,7 +66,7 @@ describe('ol.rendering.layer.VectorTile', function() {
       map = createMap('canvas');
       waitForTiles(source, {}, function() {
         expectResemble(map, 'spec/ol/layer/expected/vectortile-canvas.png',
-            IMAGE_TOLERANCE, done);
+            11.0, done);
       });
     });