Update whatsnew-3.2.rst

from https://github.com/celery/celery/commit/07ecd08a8621affde3b8ed15d118164cb26e334d commit message.

docs/whatsnew-3.2.rst

@@ -126,7 +126,7 @@ Task.replace
 
     A new builtin task (`celery.accumulate` was added for this purpose)
 
-    Closes #81
+    Closes #817
 
 
 Optimized Beat implementation