We bump the required Python version in README when an old Python release goes EOL to signal that we may break compatibility and won't shoulder the support burden any more, but AFAIK we never introduced any new feature from py36 (because py35 or even py34 was pleasant enough to work with already). Also the version in nuspec is just the absolute minimum version, so since 4.3.2 has passed review already I'll just leave it. I'll bump the Python version for future releases.