update isort

[jugmac00]

isort underwent a major update, from version 4 to version 5

Zope currently pins isort to < 5.

Maybe there is a chance at next week's sprint to update the used isort version.

Also, if #891 gets accepted, I'd favor running isort also via pre-commit.

Just in case - this snipped would do the trick:

  - repo: https://github.com/timothycrosley/isort
    rev: 5.5.3
    hooks:
    - id: isort

[dataflake]

Just for context: The only reason isort is still pinned here is because isort 5 requires a ton of code changes. This is not complicated, just a lot of work and a lot of checking and a lot of eyeballing code changes. Those code changes are all cosmetic, so it has not been a priority. Pinning isort let's Travis stay green until someone takes the time to take this on. If you want to do it that's great.

How to run isort is an entirely separate issue. Just like with flake8 in #891 I am strongly against moving it out of tox.ini.