Fix broken Compass link in the README file.
Fix broken Compass link in the README file.

rstacruz/sinatra-assetpack,jwhitcraft/sinatra-assetpack,rstacruz/sinatra-assetpack,flywithmemsl/sinatra-assetpack,flywithmemsl/sinatra-assetpack,rstacruz/sinatra-assetpack,flywithmemsl/sinatra-assetpack,jwhitcraft/sinatra-assetpack,jwhitcraft/sinatra-assetpack