Update whitenoise to 3.3.1

[pyup-bot]

There's a new version of whitenoise available.
You are currently using 3.2.3. I have updated it to 3.3.1

These links might come in handy: PyPI | Changelog | Homepage

Changelog

3.3.1

---

• Fix issue with the immutable file test when running behind a CDN which rewrites
  paths (thanks lskillen).

3.3.0

---

• Support the new immutable <https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-ControlRevalidation_and_reloading>_
  Cache-Control header. This gives better caching behaviour for immutable resources than
  simply setting a large max age.

Got merge conflicts? Close this PR and delete the branch. I'll create a new PR for you.

Happy merging! 🤖