[DOCS] Fix typo for Python section on unifying Kafka streams

1) kafkaStreams is a list.  The list should be unpacked when passing it into the streaming context union method, which accepts a variable number of streams.
2) print() should be pprint() for pyspark.

This contribution is my original work, and I license the work to the project under the project's open source license.

Author: chriskang90 <[email protected]>

Closes #9545 from c-kang/streaming_python_typo.

(cherry picked from commit 874cd66)
Signed-off-by: Sean Owen <[email protected]>

Author: chriskang90

docs/streaming-programming-guide.md

@@ -1948,8 +1948,8 @@ unifiedStream.print();
 {% highlight python %}
 numStreams = 5
 kafkaStreams = [KafkaUtils.createStream(...) for _ in range (numStreams)]
-unifiedStream = streamingContext.union(kafkaStreams)
-unifiedStream.print()
+unifiedStream = streamingContext.union(*kafkaStreams)
+unifiedStream.pprint()
 {% endhighlight %}
 </div>
 </div>