wercker.yml pipeline

made some improvements to your wercker.yml

- putting compass in a Gemfile and running the bundle-install step is definitely the way to go as you did!

- also needed to install bower and run bower install

- added 'bundleExec: true' in the Grunfile (see: https://github.com/gruntjs/grunt-contrib-compass#bundleexec)

this should result in a green build!