Hotfix - missing beautifulsoup4 from requirements/dependencies

We inadvertently took a hard dependency on beautifulsoup4 but didn't have it in our dependencies.
Unfortunately, since bs4 is in our test dependencies this passed all the tests so didn't spot it until later.

What's Changed

• Add bs4 to requirements by @ianhelle in #501

Full Changelog: v2.1.0...v2.1.1