Update @storybook/preact to support Preact 10

[fjorgemota]

Is your feature request related to a problem? Please describe.
Preact 10 is already a few months old, but, at least according to @storybook/preact's peerDependencies, it's not supported by Storybook yet. However, that module seems to work fine with latest Preact 10...

Describe the solution you'd like
Check if Preact 10 definitely works fine with @storybook/preact and update peerDependencies to reflect that.

Are you able to assist bring the feature to reality?
Assuming that the test suite already covers @storybook/preact successfully, I think I can try to update the peerDependencies requirement and verify if everything still works fine.

Additional questions
Do we will still support Preact 8? Or just support Preact 10 from now on? Again, according to my experience, Preact 10 works just fine with Storybook..and according to what I saw Storybook doesn't use too much from Preact too, so I think that this compatibility could be preserved for more time without problems.

[shilman]

@fjorgemota would you mind submitting a PR with that one-line change?

[fjorgemota]

Closed by #10978.

[shilman]

Huzzah!! I just released https://github.com/storybookjs/storybook/releases/tag/v6.0.0-beta.21 containing PR #10978 that references this issue. Upgrade today to try it out!

You can find this prerelease on the @next NPM tag.

[fjorgemota]

Nice! Thanks!