Fix webpack configuration for serving the build.
Fix webpack configuration for serving the build.

This broke when creating the `build:dev` gulp target since both dev and
serve both reference the same `webpack.conf.js` configuration file. This
commit reverts the change so that files are compiled into the .tmp
folder where the `serve` target expects them to be.

nimbis/s3commander,nimbis/s3commander,nimbis/s3commander,nimbis/s3commander