Use `git diff` and `grep` to selectively lint changed files

lint-diff-package.json

{
  "scripts": {
    "jshint:branch": "jshint $(git diff --name-only --diff-filter=ACMRTUXB $(git merge-base head master) | grep '.js$') || true",
    
    "jshint:diff": "jshint $(git diff --name-only --diff-filter=ACMRTUXB | grep '.js$') || true",
    
    "jshint:prev": "jshint $(git diff head~1 --name-only --diff-filter=ACMRTUXB | grep '.js$') || true",
    
    "coffeelint:diff": "coffeelint $(git diff --name-only --diff-filter=ACMRTUXB | grep '.coffee$') || true"
  }
}