fix import order in DataframeSuite

Author: yjshen

sql/core/src/test/scala/org/apache/spark/sql/DataFrameSuite.scala

@@ -17,10 +17,9 @@
 
 package org.apache.spark.sql
 
-import org.apache.spark.sql.catalyst.plans.logical.OneRowRelation
-
 import scala.language.postfixOps
 
+import org.apache.spark.sql.catalyst.plans.logical.OneRowRelation
 import org.apache.spark.sql.functions._
 import org.apache.spark.sql.types._
 import org.apache.spark.sql.test.{ExamplePointUDT, ExamplePoint}