Enable devServer port to customize

[mimoning]

• I ran npm test for the package I'm modifying

But something goes wrong! And I think that is not my fault…I don't know why

• I used npm run commit instead of git commit

I can't find this command…

• I have rebased my branch onto master before merging

Enable devServer port to customize. We can use PORT=xxxx npm start to run our app in a customized port.

[jvanbruegge]

Thanks for the PR, note however, if you want to be able to customize more, use the one-fits-all flavor, as it was designed for extension

[mimoning]

OK👌，thank you very much！