text: Title: Dateutil version bump
  Body: `python-dateutil` is pinned at 2.6.0, but it's starting to [conflict with some things](https://github.com/spulec/freezegun/issues/333) like `freezegun` that would like a newer version.  It seems like dependabot has been been fighting for this a while too: https://github.com/Miserlou/Zappa/pulls?q=is%3Apr+dateutil+is%3Aclosed
  
  I couldn't locate much rationale for this being pinned, could it be bumped to `>=2.7.0`?