Add rake task to purge old builds.
Add rake task to purge old builds.

integrity/integrity,faradayio/ci1,forresty/integrity,factorylabs/integrity,erik-escobedo/integrity,forresty/integrity,integrity/integrity,dkastner/prism_ci,p/integrity,integrity/integrity,erik-escobedo/integrity,p/integrity,factorylabs/integrity,faradayio/ci1