Random RDD creation example fix in MLlib statistics programming guide - mllib-statistics.md

Creating Random RDDs had the follow line in the example for Random Data Generation in the MLlib statistics programming guide:

val u = normalRDD(sc, 1000000L, 10)

It should be :

val u = RandomRDDs.normalRDD(sc, 1000000L, 10)

It applies to both the Scala and Java examples.