[SPARK-11751] Doc describe error in the "Spark Streaming Programming Guide" page
[SPARK-11751] Doc describe error in the "Spark Streaming Programming Guide" page

In the **[Task Launching Overheads](http://spark.apache.org/docs/latest/streaming-programming-guide.html#task-launching-overheads)** section,
>Task Serialization: Using Kryo serialization for serializing tasks can reduce the task sizes, and therefore reduce the time taken to send them to the slaves.

as we known **Task Serialization** is configuration by **spark.closure.serializer** parameter, but currently only the Java serializer is supported. If we set **spark.closure.serializer** to **org.apache.spark.serializer.KryoSerializer**, then this will throw a exception.

Author: yangping.wu <wyphao.2007@163.com>

Closes #9734 from 397090770/397090770-patch-1.

(cherry picked from commit 7276fa9aa9d2eccb6aebd5c690ac334699142f1e)
Signed-off-by: Sean Owen <291c18f3fb7528c712d9098b0e50a515ea0b91d5@cloudera.com>

haowu80s/spark,haowu80s/spark,haowu80s/spark,haowu80s/spark,haowu80s/spark,haowu80s/spark