Clarified the upcoming breaking change will apply to a future release. (#370)

Author: DBirtolo-mdb

source/whats-new.txt

@@ -32,8 +32,8 @@ Upcoming Breaking Changes
 
 - `MapReduceIterable <{+api+}/apidocs/mongodb-driver-sync/com/mongodb/client/MapReduceIterable.html>`__
   and map-reduce methods on `MongoCollection <{+api+}/apidocs/mongodb-driver-sync/com/mongodb/client/MongoCollection.html#mapReduce(com.mongodb.client.ClientSession,java.lang.String,java.lang.String)>`__
-  are deprecated in MongoDB v4.2 and later,  and will be replaced by the 
-  aggregation framework.
+  are deprecated in MongoDB v4.2 and later. They will be replaced by the
+  aggregation framework and removed in a future release.
 
 .. _version-4.9: