[SPARK-9601] [DOCS] Fix JavaPairDStream signature for stream-stream and windowed join in streaming guide doc

Author: Namit Katariya <katariya.namit@gmail.com>

Closes #7935 from namitk/SPARK-9601 and squashes the following commits:

03b5784 [Namit Katariya] [SPARK-9601] Fix signature of JavaPairDStream for stream-stream and windowed join in streaming guide doc