Fix the bug of getting the wrong current flow QPS in ClusterFlowChecker (#972)

sentinel-cluster/sentinel-cluster-server-default/src/main/java/com/alibaba/csp/sentinel/cluster/flow/ClusterFlowChecker.java

@@ -64,7 +64,7 @@ final class ClusterFlowChecker {
             return new TokenResult(TokenResultStatus.FAIL);
         }
 
-        double latestQps = metric.getAvg(ClusterFlowEvent.PASS_REQUEST);
+        double latestQps = metric.getAvg(ClusterFlowEvent.PASS);
         double globalThreshold = calcGlobalThreshold(rule) * ClusterServerConfigManager.getExceedCount();
         double nextRemaining = globalThreshold - latestQps - acquireCount;