Recursively remove builds in clobber task (#100)

Author: abevoelker

lib/tasks/cssbundling/clobber.rake

@@ -1,7 +1,7 @@
 namespace :css do
   desc "Remove CSS builds"
   task :clobber do
-    rm_rf Dir["app/assets/builds/[^.]*.css"], verbose: false
+    rm_rf Dir["app/assets/builds/**/[^.]*.css"], verbose: false
   end
 end