update ckeditor.js

[fedtti]

fix to issue ckeditor/ckeditor5#2178 in a more React-ly way

[Reinmar]

Hi! Thanks for As commented in https://github.com/ckeditor/ckeditor5-build-classic/issues/88#issuecomment-538950681, perhaps this is a good change, but I'd like to know why suddenly you and @woto stumbled upon this issue. No one was reporting anything like that so far.

[Reinmar]

Marking as R- until we figure out whether this change is really needed.

[tlconnor]

The before/after states of this pull request are semantically equivalent so this change should not be necessary.

I hit this same problem myself, and found that it only occurs when using rails / webpacker:
rails/webpacker#1865

From what I can tell, the problem is that webpacker with run imported modules through babel, meaning the ckeditor code gets passed through babel twice. The webpacker documentation covers this situation:
https://github.com/rails/webpacker/blob/master/docs/v4-upgrade.md#excluding-node_modules-from-being-transpiled-by-babel-loader

If the webpacker configuration change is not acceptable an alternative solution is to build the editor yourself:
https://ckeditor.com/docs/ckeditor5/latest/builds/guides/integration/advanced-setup.html

Given that the problem is somewhere within webpacker / babel, I would recommend closing this pull request.