Improve untracked files message during eject

Created by: ryouaki

> react-scripts eject

? Are you sure you want to eject? This action is permanent. Yes
This git repository has untracked files or uncommitted changes:

  ?? .gitignore,  ?? app.js,  ?? bee/,  ?? package-lock.json,  ?? package.json,  ?? views/

Remove untracked files, stash or commit any changes, and try again.

npm version is 5.0.3