Storybook 6.4 support

[maddesigns]

I got a Storybook HTML 6.4.0-beta.13 error for each story:

 Error: page.evaluate: Evaluation failed: TypeError: storybookClientApi.store is not a function
           at emitSetCurrentStory (eval at evaluate (:3:1339), <anonymous>:10:36)
           at t.default.evaluate (<anonymous>:3:1362)
           at t.default.<anonymous> (<anonymous>:1:44)

Anything I’m missing in my setup?

[ahuth]

This project uses storybookClientApi.store to display a story, which is an internal Storybook API. My guess is Storybook 6.4 will change the API.

2 options I see for moving forward:

• Use Storybook 6.3
• Try to figure out what the new API for showing a story is, and update it in

  axe-storybook-testing/src/browser/StorybookPage.ts

  Line 84 in 1b7d2bd

  store._channel.emit('setCurrentStory', {

  . Updating our dependency on @storybook/client-api may help with this.

I'll probably wait to release a version supporting Storybook 6.4 until that version is out of beta and officially released.

[maddesigns]

I stay on 6.3 for now.

[ahuth]

Once Storybook 6.4 is released (storybookjs/storybook#15355), I'll merge #46 and publish a new major version of axe-storybook-testing that supports it.