pubsub: update to pubsub example to v1beta2
pubsub: update to pubsub example to v1beta2

Change-Id: I6e960d08527a911c3b1850a6333409c6377c58df
Reviewed-on: https://code-review.googlesource.com/2450
Reviewed-by: Glenn Lewis <13a1c799ae0d2ab8fa6a3294896d9a3ccca89794@google.com>

digideskio/google-api-go-client,odeke-em/google-api-go-client,t9nf/google-api-go-client,googleapis/google-api-go-client,likaiwalkman/google-api-go-client,googleapis/google-api-go-client,krsjoseph/google-api-go-client,google/google-api-go-client,skyeunknown084/gmail-api,google/google-api-go-client,evandbrown/google-api-go-client,webhost/google-api-go-client,stems/google-api-go-client,80nashi/google-api-go-client,peterkshultz/google-api-go-client,stephenwithav/google-api-go-client