fix code style issue

Author: zjffdu

mllib/src/main/scala/org/apache/spark/ml/source/libsvm/LibSVMRelation.scala

@@ -20,7 +20,6 @@ package org.apache.spark.ml.source.libsvm
 import java.io.IOException
 
 import com.google.common.base.Objects
-
 import org.apache.hadoop.fs.{FileStatus, Path}
 import org.apache.hadoop.io.{NullWritable, Text}
 import org.apache.hadoop.mapreduce.{RecordWriter, TaskAttemptContext}