Fix Java example in Streaming Programming Guide

"val conf" was used instead of "SparkConf conf" in Java snippet.

Author: Santiago M. Mola <santi@mola.io>

Closes #2472 from smola/patch-1 and squashes the following commits:

5bfeb9b [Santiago M. Mola] Fix Java example in Streaming Programming Guide

docs/streaming-programming-guide.md

@@ -138,7 +138,7 @@ import org.apache.spark.streaming.api.java.*;
 import scala.Tuple2;
 
 // Create a local StreamingContext with two working thread and batch interval of 1 second
-val conf = new SparkConf().setMaster("local[2]").setAppName("NetworkWordCount")
+SparkConf conf = new SparkConf().setMaster("local[2]").setAppName("NetworkWordCount")
 JavaStreamingContext jssc = new JavaStreamingContext(conf, new Duration(1000))
 {% endhighlight %}