doc: Fix incorrect comment of rollingCounterInSecond in StatisticNode (#2064)

sentinel-core/src/main/java/com/alibaba/csp/sentinel/node/StatisticNode.java

@@ -90,7 +90,7 @@ import com.alibaba.csp.sentinel.util.function.Predicate;
 public class StatisticNode implements Node {
 
     /**
-     * Holds statistics of the recent {@code INTERVAL} seconds. The {@code INTERVAL} is divided into time spans
+     * Holds statistics of the recent {@code INTERVAL} milliseconds. The {@code INTERVAL} is divided into time spans
      * by given {@code sampleCount}.
      */
     private transient volatile Metric rollingCounterInSecond = new ArrayMetric(SampleCountProperty.SAMPLE_COUNT,