[Ember] Ember serve or Ember build
As most of us know that we can invoke ember s to run ember application.
Steps are ember serve will trigger ember build to build the application to dist (default) directory first, then run express server to server ember application.
It checks local server exists or not by `existsSync`, if it exists, local server will override ember’s default behavior. One can generate server by running `ember g server`, and delete server by `rm server`
I guess such option does not exist to override `ember build`, since In https://github.com/ember-cli/ember-cli/blob/master/lib/tasks/build.js, it does not check existence of such build file.
Also worthy knowing that, since build does not care about ./server directory, server directory will be ignore and not effect anything when run `ember build`.