Explicitly specify buildScan return type

[pfcoperez]

Because of type inference, not explicitly providing providing a return type for:

def buildScan(requiredColumns: Array[String], filters: Array[Filter])

... gives it the return type ScalaEsRowRDD which is a compatible type with the overridden method but limits further overriding on which some transformation is performed by the means of Spark. e.g:

org.evilcorpt.spark.sql

class SomeNewClass(...) extends ElasticsearchRelation(...) {
...
    def buildScan(requiredColumns: Array[String], filters: Array[Filter]): RDD[Row] =
        super.buildScan(requiredColumns, filters).map(someTransformationFunction)
...
}

[jbaiera]

Everything looks good to me. Thanks for the PR!

[pfcoperez]

@jbaiera Thanks to you for merging it 😄