Fix documentation of Vue 3 demo documentation

[marciogurka]

Forum post

Following the guide for setting up the Vue project you'll see that the events are not being displayed correctly, even that you follow all the steps provided there.

[ocratravis]

+1. This has been open for almost five months. I'm evaluating Bryntum Calendar for possible use in our app, and I can't even get the "hello world" example to work. Very frustrating.

[matsbryntse]

Sorry about the delay, we'll prioritize this now to get it fixed very soon. Meanwhile, if you can post in our forums about the issue you're having with your hello world example, we'll do our best to assist you.

/Mats

[SergeyMaltsev]

@matsbryntse We have this issue to support project in Vue 3.
This require API changes.
#4516

[jsakalos]

The original problem was fixed with another issue so the above PR only improves the guide.