A ktlint pre-commit hook

Usage:

repos:
- repo: https://github.com/maltzj/ktlint-pre-commit
  sha: e5bee17 
  hooks:
      - id: ktlint

Notes:

• This file stores ktlint in a .cache/ directory so that it doesn't need to be re-downloaded each time. You will probably want to add .cache/ to the .gitignore file of the project which uses this hook.
• The first time this hook runs it will need to download ktlint, which takes a long time.