call top level ActiveSupport module

otherwise it fails with:

```
/Users/troex/.bundle/gems/puff-0.3.0/lib/puff/Instrumentation/redis.rb:8:in `logging': uninitialized constant Redis::ActiveSupport::Notifications (NameError)
```

Rails 3.2.12, Ruby 1.9.3p448


Nice instrumentation hack, I like it!