Add lint:changed script entry to lint only changed files (#7055)

package.json

@@ -34,6 +34,8 @@
     "sentry:publish": "node ./development/sentry-publish.js",
     "lint": "eslint . --ext js,json",
     "lint:fix": "eslint . --ext js,json --fix",
+    "lint:changed": "{ git ls-files --others --exclude-standard ; git diff-index --name-only --diff-filter=d HEAD ; } | grep --regexp='[.]js$' --regexp='[.]json$' | tr '\\n' '\\0' | xargs -0 eslint",
+    "lint:changed:fix": "{ git ls-files --others --exclude-standard ; git diff-index --name-only --diff-filter=d HEAD ; } | grep --regexp='[.]js$' --regexp='[.]json$' | tr '\\n' '\\0' | xargs -0 eslint --fix",
     "mozilla-lint": "addons-linter dist/firefox",
     "watch": "cross-env METAMASK_ENV=test mocha --watch --require test/setup.js --reporter min --recursive \"test/unit/**/*.js\" \"ui/app/**/*.test.js\"",
     "devtools:react": "react-devtools",