v2.0.0: Merge pull request #15 from ButterCMS/chore/update-dependencies

Update dependencies:
Dependency | Old version | New version
buttercms-python | 1.3.* | 2.0.0
django-environ | 0.10.0 | 0.11.2
django | 3.2.* | 4.2.*
gunicorn | 21.2.0 | 22.0.0
psycopg2 | 2.9.7 | 2.9.9
whitenoise | 6.5.0 | 6.6.0