fix(datadog) correct valid sample_rate range
fix(datadog) correct valid sample_rate range

The sample_rate parameter for datadog represents sample rate
according to the statsd standard. As such, its valid range
is between 0 and 1.

See:
* https://docs.datadoghq.com/developers/faq/dog-statsd-sample-rate-parameter-explained/
* https://thenewstack.io/collecting-metrics-using-statsd-a-standard-for-real-time-monitoring/

Mashape/kong,Kong/kong,Kong/kong,Kong/kong