a temporary fix to copy over css files after they are generated

fixes https://github.com/meltmedia/generator-express-static/issues/6

What is causing the issue:

The css files are generated AFTER a request has been made, so if you were to copy before karma runs, the css files have not yet been generated. (the request fires off the css generators to compile the css)

A more future proof solution would to have a build step in grunt for the css files.