pubsub: OpenCensus stats signature change
pubsub: OpenCensus stats signature change

stats.Int64Measure no longer returns an error as of:
census-instrumentation/opencensus-go#641

Change-Id: I14340f8c0d975c84143dae745be60cfd0c5a4003
Reviewed-on: https://code-review.googlesource.com/25970
Reviewed-by: Jonathan Amsterdam <e3d3698b2ccd5955e4adf250d0785062d0f9018b@google.com>

googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go