Set release date of 3.6.5 to today

Update Gemfile.lock for nanoc 3.6.4

Set 3.6.3 release date to today

Set release date of 3.6.2 to today

Update release notes for 3.6.1

Fix crash in stale check when prune config is incomplete

Set release date of 3.5.0

Update version to 3.5.0b2

Make gem test remove existing gem files

Set release date for 3.4.3 to today