message: metrics service: fix spelling
  Description: fixing a spelling mistake I found while reading this code.
  Risk Level: low
  Testing: n/a
diff: @@ -56,8 +56,8 @@ void MetricsServiceSink::flushGauge(const Stats::Gauge& gauge) {
  metric->set_timestamp_ms(std::chrono::duration_cast<std::chrono::milliseconds>(
  time_source_.systemTime().time_since_epoch())
  .count());
  - auto* gauage_metric = metric->mutable_gauge();
  - gauage_metric->set_value(gauge.value());
  + auto* gauge_metric = metric->mutable_gauge();
  + gauge_metric->set_value(gauge.value());
  }
  void MetricsServiceSink::flushHistogram(const Stats::ParentHistogram& envoy_histogram) {
  