Update blowdryer-diffplug to 9.0.0.

[nedtwigg]

If you only changed documentation or typos, you can ignore the following.

After creating the PR, please update the CHANGELOG.md. We follow keep a changelog conventions, everything you need to know is below:

## [Unreleased]
### Added (or Changed, Deprecated, Removed, Fixed, Security)
- Bullet point for your change ([#1](https://link-to-your-pr))

### Changed (add a header for your entry as necessary)

We won't look at your PR until you update the changelog. We can always the change the changelog before merging, but it's easier for us to review if you have already condensed the scope of your changes into the changelog.