Add isort to pre-commit hooks

[klamann]

We should use a consistent style for import statements. Proposed config:

repos:
  - repo: https://github.com/pycqa/isort
    rev: 5.10.1
    hooks:
      - id: isort
        args: ['--py', '38', '--line-length', '100', '--multi-line', '3']

[johnnylarner]

Hey, I'd take this for the hackathon!