Remove overriding `output.path` to "/" when using CLI
Remove overriding `output.path` to "/" when using CLI

The assignment was originally to enforce linux style paths, because the prev versions of memory-fs doesn't support windows style paths.
But as it supports it now it should be fine to remove this.

Ref #337

webpack/webpack-dev-server,bdwain/webpack-dev-server,bdwain/webpack-dev-server,webpack/webpack-dev-server