Build Buck targets with deep builds

This ensures that all transitive dependencies are
available once a build is complete. It probably does
not matter in our setup, but it might in the future.

rake-tasks/buck.rb

@@ -221,7 +221,7 @@ def buck(*args, &block)
 
   if task.class == Rake::FileTask && !task.out
     task.enhance do
-      Buck::buck_cmd.call('build', [task.name])
+      Buck::buck_cmd.call('build', ['--deep', task.name])
     end
 
     Buck::enhance_task(task)