problems occurred when no local webpack-dev-server is installed

[zzzgit]

#806
#729

I have reported 2 problems,they are both caused by that no local webpack-dev-server is installed.
In this situation,it should give the users a warn or an error in the console.

[SpaceK33z]

webpack-dev-server doesn't do anything with loaders, it passes everything to webpack itself. So I can't fix that in here. Also note that I would recommend against installing webpack locally but installing webpack-dev-server globally. That's just asking for trouble.

[jcrben]

I recommend closing this. Maybe someone should be throwing better errors, but it doesn't seem like it's this library.