Get `plugin` javadoc to point to `lib`

We publish the `plugin` and `lib` at the exact same time, and I can't figure out how to get the plugin javadoc to correctly point to the `lib` javadoc.

e.g. [`Changelog ChangelogExtension::getParsedChangelog()`](https://javadoc.io/static/com.diffplug.spotless-changelog/spotless-changelog-plugin-gradle/1.1.0/com/diffplug/spotless/changelog/gradle/ChangelogExtension.html#getParsedChangelog--)