fix

Author: jinxing

core/src/main/java/org/apache/spark/shuffle/sort/UnsafeShuffleWriter.java

@@ -17,10 +17,10 @@
 
 package org.apache.spark.shuffle.sort;
 
+import javax.annotation.Nullable;
 import java.io.*;
 import java.nio.channels.FileChannel;
 import java.util.Iterator;
-import javax.annotation.Nullable;
 
 import scala.Option;
 import scala.Product2;