FPGrowthModel.transform should skip duplicated items

scala> val data = spark.read.text("data/mllib/sample_fpgrowth.txt").select(split($"value", "\\s+").alias("features")) 
data: org.apache.spark.sql.DataFrame = [features: array<string>]

scala> val data = spark.read.text("data/mllib/sample_fpgrowth.txt").select(split($"value", "\\s+").alias("features")) 
data: org.apache.spark.sql.DataFrame = [features: array<string>]

scala> fpm.transform(Seq(Array("t", "s")).toDF("features")).show(1, false)
+--------+---------------------+
|features|prediction           |
+--------+---------------------+
|[t, s]  |[y, x, z, x, y, x, z]|
+--------+---------------------+