You are actualy listening on localhost only.
To be reachable from outside replace the following line in your package.json file:
"start": "webpack-dev-server --inline --content-base ."
by :
"start": "webpack-dev-server --host 0.0.0.0 --inline --content-base ."
Related discussion : https://github.com/webpack/webpack-dev-server/issues/147