fix: minor fix in vt spec

Author: fuzhenn

packages/vt/test/specs/update.spec.js

@@ -149,7 +149,7 @@ describe('update style specs', () => {
                     const pixel = readPixel(layer.getRenderer().canvas, x / 2, y / 2);
                     assert.deepEqual(pixel, [255, 0, 0, 255]);
                     done();
-                }, 200);
+                }, 400);
             }, 200);
         }, 200);
     });