add gem compass to vm

[ThomasLohner]

This is needed for scss compilation in symfony2

fix:

sudo apt-get install ruby-dev
sudo gem install compass

[jkrug]

Is Scss the Symfony2 Standard?

[ThomasLohner]

Don't know, at least ongr uses this. On Live-Systems we can do assetic dump in the build process. But on DEV machines we need compass.