Summary:
Based on https://github.com/gristlabs/grist-core/pull/251. It may not look like it, but there's very little going on in this diff:
- Tweak the DATEVALUE doctest for Python 2/3 compatibility.
- Mirrors the PR's changes to requirements3.txt in requirements.txt, i.e. make the same dependency upgrades in Python 2.
- Make the same upgrades in the thirdparty folder for the Python 2 nacl sandbox.
Test Plan: Updated one doctest for dateutil. Checked changelog of sortedcontainers. html5lib is only used by messytables and isn't actually relevant.
Reviewers: paulfitz
Reviewed By: paulfitz
Differential Revision: https://phab.getgrist.com/D3609