Fix SPARK-1695: java8-tests compiler error: package com.google.common.collections does not exist

Author: witgo

extras/java8-tests/src/test/java/org/apache/spark/Java8APISuite.java

@@ -23,7 +23,7 @@
 
 import scala.Tuple2;
 
-import com.google.common.collections.Iterables;
+import com.google.common.collect.Iterables;
 import com.google.common.base.Optional;
 import com.google.common.io.Files;
 import org.apache.hadoop.io.IntWritable;