Our Storybook dependencies have been updated to v6.1.9, from v5. This
was done to address a security vulnerability in a transitive dependency
of these packages (`highlight.js`).
The primary changes required by this Storybook update were the change
in import path for the `withKnobs` hook, the change in background
config format, and the webpack configuration. Storybook seems to work
correctly.
The migration was guided by the Storybook changelog[1] and the
Storybook v6 migration guide[2].
There is one Storybook error remaining; it fails to load the Euclid
font. This is a pre-existing error though, so we can fix it in a later
PR.
The `yarn.lock` file was deduplicated in this PR as well, as it was
required to fix various install warnings that were introduced with this
update.
[1]: https://github.com/storybookjs/storybook/blob/next/CHANGELOG.md
[2]: https://github.com/storybookjs/storybook/blob/next/MIGRATION.md
