Fix inverted anomaly score calculation in HSTrees classifier

Author: justinuliu

moa/src/main/java/moa/classifiers/oneclass/HSTrees.java

@@ -228,7 +228,7 @@ public double getAnomalyScore(Instance inst)
 
 			accumulatedScore = accumulatedScore / (((double) this.numTrees));
 
-			return 0.5 - accumulatedScore + this.anomalyThreshold;
+			return accumulatedScore;
 		}
 	}