SubscriberClient no longer has 'topic_path' method, but documentation still makes references to it. #209

After the update to library version 2.1.0, the SubscriberClient no longer has a 'topic_path' method. I'm assuming that was intentional, but the documentation still makes reference to it.

Here is a link to one such instance in the documentation:
https://googleapis.dev/python/pubsub/latest/subscriber/index.html#creating-a-subscription