Sentinel Fmt Hook Does Not Work

[schultzwc18]

Describe the bug
Hook fails to run when installed through pre-commit because of two bugs:

1. Line 1 must have shebang but is instead on line 2
2. sentinel fmt does not have a diff command-line argument

To Reproduce
Steps to reproduce the behavior including the relevant Terraform/Terragrunt/Packer version number and any code snippets and module inputs you used.

.pre-commit-config.yaml

repos:
  - repo: https://github.com/gruntwork-io/pre-commit
    rev: v0.1.25
    hooks:
      - id: sentinel-fmt

pre-commit install
pre-commit run --all-files

Expected behavior
Pre-commit hook would run and indicate files requiring formatting

Nice to have

• Terminal output
• Screenshots

Additional context
Add any other context about the problem here.