fix 3.2 explain plan ref

Author: jeff-allen-mongo

source/release-notes/3.2.txt

@@ -1206,7 +1206,7 @@ representing the number of index keys examined during index scans.
 Prior to 3.2, ``keysExamined`` count in some queries did not include the
 last scanned key. As of 3.2 this error has been corrected. For more
 information, see
-:data:`~explain.executionStats.executionStages.inputStage`.
+:data:`~explain.executionStats.executionStages.inputStage.keysExamined`.
 
 The diagnostic logs and the system profiler report on this statistic.