fix

Author: gy910210

samoa-api/src/main/java/org/apache/samoa/learners/InstanceUtils.java

@@ -133,7 +133,7 @@ static public Instance convertToSamoaInstance(DataInstance dataInstance) {
         } else if (dataInstance instanceof ClusterDataInstance) {
             return InstanceUtils.convertClusterInstance((ClusterDataInstance) dataInstance);
         } else {
-            throw new Error("Valid input class!");
+            throw new Error("Invalid input class!");
         }
     }
 }