[STREAMING] [DOCS] Fix wrong url about API docs of StreamingListener

A little fix about wrong url of the API document. (org.apache.spark.streaming.scheduler.StreamingListener)

Author: dobashim <[email protected]>

Closes apache#6024 from dobashim/master and squashes the following commits:

ac9a955 [dobashim] [STREAMING][DOCS] Fix wrong url about API docs of StreamingListener

Author: dobashim

docs/streaming-programming-guide.md

@@ -1915,7 +1915,7 @@ In that case, consider
 [reducing](#reducing-the-processing-time-of-each-batch) the batch processing time.
 
 The progress of a Spark Streaming program can also be monitored using the
-[StreamingListener](api/scala/index.html#org.apache.spark.scheduler.StreamingListener) interface,
+[StreamingListener](api/scala/index.html#org.apache.spark.streaming.scheduler.StreamingListener) interface,
 which allows you to get receiver status and processing times. Note that this is a developer API
 and it is likely to be improved upon (i.e., more information reported) in the future.