Update webpack to version 4.12

[ma2ciek]

Suggested merge commit message (convention)

Other: Updated webpack to version 4.12.

[ma2ciek]

I'll update one test in BalloonPanelView, as I got the following error message:

TypeError: ES Modules cannot be spied
          at Function.spy (base-dev/node_modules/sinon/pkg/sinon.js?51ef4aa3de92c43bc4721758a1e445182048177d:2342:15)
          at Object.spy (base-dev/node_modules/sinon/pkg/sinon.js?51ef4aa3de92c43bc4721758a1e445182048177d:863:34)
          at Context.it (webpack:///packages/ckeditor5-ui/tests/panel/balloon/balloonpanelview.js:176:0 <- build/.automated-tests/entry-point.js:4877:105)

[ma2ciek]

Can I change the BalloonPanelView class, so it will contain a static method getOptimalPosition which will be an alias to the original getOptimalPosition method from @ckeditor/ckeditor5-utils/src/dom/position? Then I'll be able to mock that method in tests.

https://github.com/ckeditor/ckeditor5-ui/blob/0ed2b79379e1ea78559cf16ddc0863f6546ebb69/src/panel/balloon/balloonpanelview.js#L11

cc @Reinmar

[Reinmar]

cc @oleq

[oleq]

I guess so if there's no other way ;-) Why did that thing get broken in the first place, anyway?

[ma2ciek]

We import position utils, which is a module

import * as positionUtils from '@ckeditor/ckeditor5-utils/src/dom/position';

And then we stub the module's export with:

const spy = testUtils.sinon.spy( positionUtils, 'getOptimalPosition' );

Which becames invalid now, as positionUtils is an ES Module, not a normal object. (I guess it).