Add support for justfiles

[marcaddeo]

This adds support for justfile.

Just supports recipes that contain a shebang, but unfortunately it's being interpreted as a comment line and I don't see a way to resolve it within Tokei.

# Comment
do-something:
  #!/usr/bin/env node
  console.log('im running in node')

# Comment
do-something-else:
  echo "regular recipe"

Closes #1116

[XAMPPRocky]

Thank you for your PR, and congrats on your first contribution! 🎉