Update ReleaseNotes.md

Author: mgravell

docs/ReleaseNotes.md

@@ -8,7 +8,7 @@ Current package versions:
 
 ## Unreleased
 
-- Fix #2951 - sentinel reconnection failure ([#2956 by mgravell](https://github.com/StackExchange/StackExchange.Redis/pull/2956))
+- Fix [#2951](https://github.com/StackExchange/StackExchange.Redis/issues/2951) - sentinel reconnection failure ([#2956 by mgravell](https://github.com/StackExchange/StackExchange.Redis/pull/2956))
 
 ## 2.9.17